Varnishes and Surface Coatings: Low Molecular Weight Varnishes

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Authors: Jill Whitten, Elisabeth Mention, Liisa Merz-Lê, Ruth Barach Cox, Sarah L. Fisher, Mary McGinn, Robert Proctor, Camilla Van Vooren, Michael Swicklik, Mira & Gustav Berger
Date: Submitted September, 1997
Compiler: Wendy Samet

Introduction: General Characteristics of Low Molecular Weight Resins for Picture Varnish

The characteristics of low molecular weight (LMW) resins are determined by differences in molecular weight.

LMW resins are a group of resins consisting of small molecules with average molecular weights of 500–1000 (de la Rie 1987, 4). Although the class of LMW resins includes materials that are chemically different (e.g., mastic, damar, Laropal® K80, MS2A®, Regalrez® 1094, and Arkon® P-90 are all LMW resins), they share certain common characteristics.

The smaller molecule size has a significant effect on the visual appearance and physical properties of these resins. LMW resins level well because they make solutions of low viscosity even at high concentrations and will continue to level when they are applied to artworks and dry to a smooth and glossy film. Therefore, they saturate better than polymers. Some LMW resins are more glossy than others, but they all dry in a glossy film compared to polymers.

All LMW resins used for picture varnishes are initially soluble in a solvent less polar than xylene (of the resins in this section mastic requires the strongest solvent).

Of the LMW resins, the solubility of natural resins and ketones will change the most over the long term both requiring increasingly polar solvents for removal. As LMW resins oxidize, an increase in the molecular weight may occur, but this molecular weight will still be considerably lower than the starting molecular weight of a polymer and the resins will remain soluble as they age (Maines, personal communication, 1997). LMW resins have relatively high glass transition temperatures and are generally brittle. They all have relatively high refractive indices.

Natural Resin Varnishes

Mastic

[terpene resin]

Historical Background

Mastic has been used in crafts since antiquity. In Greece it is masticated (hence its name) as a kind of chewing gum.

Its use as a picture varnish extends from the 9th century (Gettens and Stout 1966), when it was formulated as an oil varnish, being boiled in linseed oil. Its use as a spirit varnish with turpentine as a diluent is recorded as early as the 16th century in Italy, and it was in use in Northern and Southern Europe by the 17th century (Van De Graaf 1958). Mastic was generally the picture varnish of choice (De Burtin 1845) and continued as such until damar varnish was first introduced in the 19th century (Feller, Stolow, and Jones 1985).

Source

(1) PHYSICAL FORM

Mastic takes the form of fragrant, translucent, straw-colored lumps known as “tears.”

(2) ORIGIN AND MANUFACTURE

Mastic resin comes from a small tree, Pistacia Lentiscus of the family Anacardiacaea, which is found growing in several areas of the Mediterranean. The finest commercial quality is collected almost exclusively from the island of Chios in the Greek Archipelago. It is harvested from vertical slits in the bark from which it originates.

(3) MANUFACTURERS AND VENDORS

Vendors include: O.G. Innes Corp., New York, NY; Kremer Pigments, New York NY; Fezandie & Sperrle, Supplied by Benbow Chemical Packaging, Inc., Syracuse, NY; and A.F. Suter & Company, Ltd., London, UK. [See Appendix II, Vendor Directory.] These suppliers sell the resin in “tear” form.

Prepared mastic varnish in turpentine has been available until recently in this country and may still be obtained from Winsor & Newton's European catalog; however, according to representatives of the manufacturer (Winsor & Newton), heat is employed in its preparation, which is not advised in traditional recipes as it increases the tendency of the resin to yellow (De Burtin 1845, 297; Doerner 1962, 131).

Chemical and Physical Properties

(1) CHEMICAL CLASSIFICATION:TRITERPENOID RESIN

(2) CHEMICAL FORMULA/STRUCTURE

Mastic, being a natural resin, has a varied and complex composition, varying with its age and origin. As a terpene resin, it is built up from the isoprene unit, and is composed of six of these units. The following three examples of the structure have been identified:

Components in the resin which have been isolated and characterize mastic are euphane, oleanic acid, and a bicyclic diol (Mills and White 1994).

(3) MOLECULAR WEIGHT

Weight average molecular weight: 1,929

Number average molecular weight: 460 (de la Rie 1987,4)

(4) REFRACTIVE INDEX: 1.536

(5) SOLUBILITY

Shell Odorless Mineral Spirits/Shell Sol® 71	I
Stoddard Solvent/Shell Sol® 340 HT	I
Shell Mineral Spirits 145	I
Petroleum Benzine	I
Turpentine	SR
Shell Cyclo Sol® 100/Shell Cyclo Sol® 53	SR

Xylenes	SR
Toluene	SR
Isopropanol	SR
Ethanol	SR
Acetone	SR
Arcosolv® PM/1-Methoxy-2-propanol	SR

Terms

S	Soluble	clear solution
SC	Soluble Cloudy	completely dissolved, slightly cloudy solution
SV	Soluble Viscous	clear, highly viscous solution
SR	Soluble Residue	residue on the bottom
PSG	Partially Soluble Gel	resin is dissolved in a clear soft gel in a two-phase mixture with solvent on top
PIG	Partially Soluble Immobile Gel	resin is dissolved in a hard gel in a two-phase mixture with solvent on top
IM	Insoluble Milky	insoluble but a minute fraction has swollen and whitened, solvent looks milky
IC	Insoluble Clear	insoluble but a small portion of the resin has swollen to the point that it is stuck to the bottom of the jar, solvent is clear
I	Insoluble	insoluble, undissolved resin sits in clear solvent

Examples: S to PSG = mostly soluble; PIG to I = mostly insoluble

See also Appendix I, Solubility Testing Description and Solvents Used in Testing.

(6) GLASS TRANSITION TEMPERATURE (Tg)-34.7°C

With 3% Tinuvin® 292, the Tg is lowered to 31.9°C (de la Rie 1990, 163).

(7) BRITTLENESS AND FLEXIBILITY

Characterized as brittle, mastic resin dissolved in turpentine was coated on aluminum foil to a thickness of 1.5 mil. Foil was placed around mandrels of varying diameters to determine at what diameter cracking was observed. The strips were placed on the mandrels at 70°F and 50% RH with the following results:

Diameter of mandrel in inches:

Strips normally dried for one month	1.9
Strips bake dried at 158°C for two days	2.5
(Feller 1958, 164)

As noted above, when Tinuvin® 292 is added at 3% weight/weight, the Tg is lowered, which reduces the brittleness (de la Rie and McGlinchey 1990, 164).

Preparation/Formulation

(1) TYPICAL BRUSH SOLUTION

Many traditional recipes for mastic varnish call for proportions of resin to turpentine of 25–50% weight to volume (Wehlte 1967, 398; Doerner 1934, 131). However, an informal survey of conservators in this country using mastic shows a preference for much thinner solutions, ranging from 3–10% weight/weight in turpentine. The following is a recipe for formulating a stock solution of approximately 7% resin to turpentine:

3 1 of Winsor & Newton English Distilled Turpentine® (2,640 g)

264 g Chios mastic resin

Note: Approximately 3% of the resin will remain undissolved and be discarded, hence the apparent discrepancy of the above proportions in preparing a 7% solution.

Method: Select the lightest colored pieces, discarding any very discolored ones. Place in a bag made of loosely woven polyester or other fabric. (A nylon stocking makes an ideal container.) Suspend the bag of resin in an amber colored jar into which the turpentine has been added. Cover the jar and allow the resin to dissolve slowly. This may take from two days to a week or more, depending upon the freshness of the mastic. The jar should be gently agitated several times a day by rotating it in small circles.

Do not insist upon complete dissolution of the resin; there will be a small amount of material left in the bag and this should be discarded.

The varnish will be somewhat cloudy at first, but allow it to settle for several days and a clear solution will result. A residue should remain in the bottom of the jar. Pour off the clear varnish and use as is, or dilute further.

(2) TYPICAL SPRAY SOLUTION

Same as brush solution.

(3) ADDITIVES

Tests indicate that to stabilize mastic varnish, ultraviolet light should be eliminated. A hindered amine light stabilizer (HALS), Tinuvin® 292 from Ciba-Geigy, has proven effective when added at 4% to the weight of the resin (de la Rie and McGlinchey 1990). This proportion can be reached by adding nine drops to 100 g of the stock solution. It should be added shortly before applying the varnish (rather than adding it to the stored solution).

(4) STORAGE/SHELF LIFE

Practitioners report that the fresher the mastic, the more easily it dissolves. For this reason, buying it in relatively small quantities is recommended. The dry resin should be stored in a cool, dry place. Once dissolved in turpentine, it begins to oxidize and should be stored in a tightly covered dark jar. The prepared varnish should be used within a six-month period, or before it begins to yellow and thicken.

Working Characteristics and Practical Properties

(1) APPEARANCE

Mastic's low molecular weight forms a very level film, giving superior saturation of color and gloss and high distinction of image.

(2) BRUSHING

The varnish benefits from its relatively long working time, allowing the brushing out to be carried on virtually to the no flow point. When used in a thin solution (approximately 5–10% weight/weight resin to turpentine), the brushing out should take 5–20 minutes, depending on the size of the picture. It will be dry to the touch within 24 hours. One can apply additional coats in this manner once the previous coat has dried (although one should wait at least one week between brush coats).

(3) SPRAYING

The spray application should be very fine, depositing an even coat over the surface. It should then be brushed briskly with a badger brush to pick up excess varnish. It will be dry to the touch in 24 hours. By building up successive layers, one can obtain an even surface without resorting to a thick layer of varnish.

(4) MODIFICATIONS/TRICKS OF THE TRADE

(a) Microcrystalline wax may be added to the varnish in small amounts to modify the gloss. The varnish should be heated gently to dissolve the wax and may be sprayed or brushed on.

(b) Benzyl alcohol added to the solution in very small quantities (approximately 10 drops to a 100 ml solution) is effective where saturation of a surface is problematic. This should be used in spray application only, never in brushed coats.

(c) Once the mastic has been applied and dried, the gloss can be altered by polishing with a silk cloth with cotton wool inside it. When further matting is required, more vigorous polishing can break down the dried mastic into a fine dust, which when rubbed into the area will give a dry appearance.

(d) In cases where obtaining an even varnish is difficult because of a pitted, dry, and uneven paint surface, mastic has been dissolved in ethanol at 20% resin to solvent weight/weight and applied in repeated, successive sprays. It will begin to dry before hitting the surface and in this way create an artificially even surface. Once dry, the mastic in ethanol coating (which should look like an even layer of snow on the surface of the painting) is sprayed with the stock 7% solution in turpentine to which a small amount of benzyl alcohol has been added. This will reform the underlying layers and result in an even varnish.

(e) A dilute solution of mastic dissolved in ethanol makes a very effective isolating varnish when used on wax fills.

Aging Characteristics

(1) CHEMICAL PROCESS

When mastic is dissolved in turpentine and spread in a film to dry, it begins to oxidize rapidly (Feller, Stolow, and Jones 1985).

(2) REMOVABILITY

Although mastic does not crosslink, the acidic compounds which result from aging change the solubility of the film, requiring more polar solvents to remove it (de la Rie 1987,2). For instance, when fresh it will dissolve in turpentine, but when aged will require a proportion of acetone or toluene for removal.

(3) AUTOXIDATION

The autoxidation process causes yellowing and loss of transparency, as well as hazing and cracking. Bloom may also result.

(4) ATTRACTION AND RETENTION OF DIRT AND GRIME

Practitioners report that mastic attracts dirt and grime to a lesser extent than do many synthetic resins.

(5) THEORETICAL LIFETIME

The mastic varnish film may exhibit defects in as short a period as 15 years (de la Rie 1987, 3). With the addition of Tinuvin® 292 and used in an ultraviolet-free environment, this period is greatly extended (de la Rie and McGlinchey 1990).

Health and Safety

Mastic resin itself presents no health hazards; however, when dissolved in turpentine, the solution can cause irritation to skin and eyes. Use with adequate ventilation and avoid contact with skin and eyes. Keep away from heat and flame.

Disposal

Dispose in accordance with local regulations for flammable waste.

Damar¹

[triterpenoid resin]

Origin and Geography

A natural, soft resin made of triterpenoid compounds, damar varnish is extracted from the Dipterocarpoideae subfamily of the Dipterocarpaceae family of trees, consisting of 15 genus and over 400 species. These trees grow from the Seychelles to New Guinea to the Philippines; however, the principal varnish resin exported to the West comes from Malaysia and Indonesia, and of the species Hopea or possibly Shorea varieties (Mills and White 1987). The principal ports are located at Singapore and Jakarta (Batavia) (Mantell, Kopf, Curtis, and Rogers 1942, 38).

In Borneo alone over 280 species are found. In India, Burma, and Thailand, only four are principally used: Balanocarpus heimii, Shorea robusta, Vateria indica, and Hopea odorata. In Sri Lanka only two main species of Doona are used (Mills and White 1987,93).

Historical Background

(1) INDUSTRIAL AND ARTISTIC USES

Before damar was used as a picture varnish, it had been used in Indonesia to coat clay vessels (Ellen and Glover 1974,353–79) and was possibly mixed with oils for musical instrument varnish in 18th-century Italy.

Damar is thought to have first been used as a varnish around 1829 and came into wider use about 15 years later (Feller 1966). Residual damar resin was found in Turner's varnish bottle, discovered in his studio after his death in 1851 (Hanson 1954, 162–73). In early documentation on damar use, the addition of rubber was recommended to stop yellowing and brittleness (Brommelle 1956, 181).

Commercially, damar was mixed with other oil media and sold as a proprietary product for oil painting. Individual artists used damar as an extender for their oil paints and as a glaze medium (Mills and White 1987, 93). Even today artists' manuals recommend that damar be mixed with media for glazing and retouching purposes (Mayer 1970, 216–17). Damar has also been suggested for use in tempera emulsions and as a pastel fixative (Gettens and Stout 1966, 16). It has been used as a varnish since the first quarter of the 19th century (Ruhemann 1968, 272).

(2) CONSERVATION USE

Damar was introduced by German restorers as a more stable material than mastic for picture varnishes (Horie 1987, 147). Over the years, it has been used by conservators as a consolidant, inpainting medium, and for varnishing. The properties of damar are well known because it has been used for such a long time, making it predictable.

Source

(1) HARVESTING AND PHYSICAL FORM

The harvesting of damar resin is a challenging procedure. The trees to be tapped must first be found among other species in a virgin forest (Masschelein-Kleiner 1985, 84). The tree should reach a maturity of 50 years before a good resin yield can be expected. Increased insect infestation in mature trees tends to create drawbacks in the collection procedures and quality of damar resin. When a suitable tree is found, it is tapped by making an incision in the trunk. Once tapped the damar resin flows in a viscous manner with an evaporating aromatic scent that continues until it hardens (Gettens and Stout 1966, 16). The rounded clumps of the light, pale yellow resin are collected and sized. Dirt, twigs, rocks, and other foreign matter are almost always found associated with damar.

(2) ORIGIN OF MANUFACTURE

Damar resin manufacture originated in Malaysia and Indonesia. The varieties of damar resins produced were often named after their shipping points: Batavia, Indonesia, or Singapore. Singapore damar is high-quality graded from No. 1 (lacking impurities and being nearly transparent in color) to No. 3., and then sorted by size. Batavia (Jakarta) damar is quality-graded principally by size from “A” (about a one-half inch sieve opening size) to “F” (powder). Generally grades “A,” “B,” and “C” are marketed in the West (Mantell et al. 1942, 38). The damar is usually dewaxed by the addition of alcohol, then agitated, then a waxy precipitate is allowed to form, before the damar is decanted off (Gettens and Stout 1966, 17).

(3) MANUFACTURERS AND VENDORS

The following types/brands are available as follows [see also Appendix II, Vendor Directory:

Utrecht Finest Pure No. 1, Singapore Damar Crystals from Utrecht Manufacturing Corp., Seattle, WA; Gum Damar Crystals from Daniel Smith, Seattle, WA; Gum Damar #1 from Conservator's Emporium, Reno, NV; Damar Resin 1 lb. from Talas, New York, NY; Damar Indonesian-100g. from Kremer Pigments, Inc., New York, NY; Grade #1 Dewaxed Damar from Sigma Chemical Company, Saint Louis, MO; and Damar Varnish, turpentine and alcohol, and Damar Retouch Varnish in White spirits and petroleum distillate from Winsor & Newton.

Chemical and Physical Properties

(1) CHEMICAL CLASSIFICATION:TRITERPENOID RESIN

(2) CHEMICAL FORMULA

Damar resin consists of two resin acids [dammarolic (C₅₆H₈₀O₈) and dammarylic (C₃₆H₆₀O₃)], a-resene (C₁₁H₁₇O), β-resene (C₃₁H₅₂O), and a small amount of a terpenic essential oil [dammaryle (C₁₀H₁₆)] (Mantell et al. 1942).

Damar consists largely of triterpenoid compounds of the tetracyclic dammarane series with proportions of polymeric hydrocarbons called β-resene and a neutral fraction once identified as the a-resene (Mills and White 1987, 93).

(3) CHEMICAL STRUCTURE

Here are three variations of the tetracyclic dammarane structures (Horie 1987, 146) (Mills and White 1987, 94):

(4) MOLECULAR WEIGHT

(a) Weight average molecular weight: 424–506¹

(b) Number average molecular weight: unknown at this time²

(5) REFRACTIVE INDEX: 1.535–1.538³

(6) GLASS TRANSITION TEMPERATURE: 67–75° C (INNES DATA SHEET)⁴

(7) BRITTLENESS AND FLEXIBILITY:

Damar is considered very brittle when well-dried (Feller, Stolow, and Jones 1985, 120–5).

(a) Yield point: unknown at this time.

(b) Break point:

6 to 1.7 inches diameter of mandrel after 1 month drying and calculated by the diameter of bending necessary to cause profuse cracking of 1.5 film on 1 mil aluminum foil at 70° F and 50% RH (Feller 1958, 162–74).

¹ 1361 (de la Rie and McGlinchey 1990, 168)

² 488 (de la Rie and McGlinchey 1990, 168)

³ 1.539 (de la Rie and McGlinchey 1990, 168)

⁴ 39.3°C (de la Rie and McGlinchey 1990, 168)

(8) SOLUBILITY

Shell Odorless Mineral Spirits/Shell Sol® 71	IC
Stoddard Solvent/Shell Sol® 340 HT	SC
Shell Mineral Spirits 145	SC
Petroleum Benzine	SC
Turpentine	SC
Shell Cyclo Sol® 100/Shell Cyclo Sol® 53	S

Xylenes	S
Toluene	SC
Isopropanol	IM
Ethanol	IM
Acetone	I
Arcosolv® PM/1-Methoxy-2-propanol	I

Terms

S	Soluble	clear solution
C	Soluble Cloudy	completely dissolved, slightly cloudy solution
SV	Soluble Viscous	clear, highly viscous solution
R	Soluble Residue	residue on the bottom
PSG	Partially Soluble Gel	resin is dissolved in a clear soft gel in a two-phase mixture with solvent on top
PIG	Partially Soluble Immobile Gel	resin is dissolved in a hard gel in a two-phase mixture with solvent on top
M	Insoluble Milky	insoluble but a minute fraction has swollen and whitened, solvent looks milky
C	Insoluble Clear	insoluble but a small portion of the resin has swollen to the point that it is stuck to the bottom of the jar, solvent is clear
I	Insoluble	insoluble, undissolved resin sits in clear solvent

Examples: S to PSG = mostly soluble; PIG to I = mostly insoluble

See also Appendix I, Solubility Testing Description and Solvents Used in Testing.

Preparation/Formulation

(1) PRACTICAL CONSIDERATIONS

Select pieces that are the most clear and clean. Some impurities are to be expected even in the highest quality damar. After the resin is dissolved in solvent, it should be filtered to remove impurities and undissolved material. The mixture may be cloudy but it is better to filter it than to add polar solvents to clear the mixture (Wehlte 1975, 399).

(2) MANUFACTURERS' RECOMMENDATIONS

Most suppliers of damar make similar recommendations for preparing the resin: turpentine as the solvent, suggested in most cases at approximately 30% weight/weight solution. The recommendations of two suppliers are summarized below:

(a) Kremer Pigments, Inc.

Supplies hand-picked Sumatra. The Kremer recipe makes a 33% weight/weight solution. Mix 100 g damar with 200 g gum turpentine. The damar crystals should be wrapped in gauze and suspended by a string into a jar with the solvent. Allow a couple of days for dissolution (Kremer recommendations 1975).

(b) Utrecht Manufacturing Corp.

Supplies Number One Singapore. Utrecht gives two recipes; one for approximately an 11% weight/volume damar solution, the other for approximately a 38% weight/weight solution.

Mix 5 lb damar with 5 gal gum turpentine

Mix 1 lb damar with 26 oz gum turpentine

Wrap the crystals in a lint-free porous cloth and submerge in a container of turpentine. Shake occasionally. Full dissolution will occur in 24–36 hours. Some cloudiness may occur due to natural wax components of damar, but the varnish will be clear and transparent when dry. Add small amounts of acetone, anhydrous alcohol, or methanol to clear up the cloudiness if desired. (Ed. note: such solvents must be incorporated with an understanding of their effect on paint layers.)

(3) TYPICAL BRUSH SOLUTIONS

Conservators most commonly prepare solutions for brushing at concentrations of damar in solvent ranging from about 10% weight/volume to 25% weight/volume (practical experience). Damar may be dissolved in turpentine or hydrocarbon mixtures of 30% weight/volume or less (see Solubility chart above). This author avoids turpentine, the traditional damar solvent, due to its impurities.

(4) TYPICAL SPRAY SOLUTIONS

Typical spray solutions used by conservators are found to be of lower percentages, between 5% and 20% weight/volume in turpentine or hydrocarbon mixtures (practical experience). Again, some avoid turpentine due to its impurities.

(5) ADDITIVES

In the past, beeswax, microcrystalline wax, or stearate (a saponified waxy crystalline substance of saturated fatty acids) was added to damar varnish formulations so that the resulting film would be of lower gloss. Frequently, matting agents, such as fumed silica, siliceous pigments, and other transparent or semitransparent particles are added to varnish solutions to generate a satiny low sheen varnish layer (Bernstein 1992, 114). Additives important to the stabilization and extended life of damar varnishes are discussed in Section VII.,A. Phenolic Antioxidants, Stabilizers, and UV Absorbers. Research indicates damar varnish can be stabilized in the absence of ultraviolet light with the addition of 3% Tinuvin® 292 to the weight of the resin (de la Rie 1990, 160–4).

(6) SPECIAL CONSIDERATIONS

Try to avoid varnishing during periods of high humidity, as this could allow for trapping of moisture and lead to the development of bloom.

(7) STORAGE/SHELF LIFE

Damar varnishes should be stored in tightly closed containers, preferably in the dark and at room temperature. Since recipes for damar varnish are relatively straightforward, small batches can be made and used within a short time. Damar in solution, with or without Tinuvin® 292, should not be stored long-term (de la Rie and McGlinchy 1989, 144). In crystalline form damar can be stored indefinitely in an air tight container in a dry and dark area. If the damar is very old, it may require a higher aromatic content solvent in order to dissolve it.

Working Characteristics and Practical Properties

(1) APPEARANCE

(a) Film Formation

During the initial drying stages, a film of damar resin will continue to flow due to its low molecular weight and low viscosity. The resin flows into and fills roughnesses in a painted surface producing a smooth glossy film (Feller 1985, de la Rie 1987, Thomson 1957).

(b) Saturation

Damar resin's low molecular weight and low viscosity characteristics are fundamental in producing a film of high refractive index. Consequently, paint layers coated with a damar varnish appear saturated in contrast to those coated with a high molecular weight and high viscosity polymer (Feller 1958, de la Rie 1987).

(c) Gloss

A damar varnish film will continue to flow, even at high concentrations of about 70–80% (Feller, Stolow, and Jones 1985, 140) producing a readily smooth high gloss surface. The gloss can be controlled by the use of additives or by the method of application. See “Modification for Special Application and Effects/Tricks of the Trade,” Section d) below.

(2) BRUSHING10–20% (WEIGHT/VOLUME)

Solvent	Working Time	Drying Time
xylene or toluene	5 to 15 min	1 to 2 weeks
TS-28 and Mineral Spirits 135	30 to 40 min	1 to 2 months

Several thin layers should be applied to build up a varnish layer that evenly coats and saturates. A single thick application will tend to be uneven and extremely glossy. To aid in making thin varnish layers, remove excess from the brush before applying the varnish. This can be done easily by skimming the brush against the edge of the varnish container or tamping the brush on a lint-free paper towel. (Turpentine will achieve a more even gloss in a thinner solution, 5–10%.)

(3) SPRAYING: 5–15% (WEIGHT/VOLUME)

Solvent	Working Time	Drying Time
xylene or toluene	5 to 15 min	1 weeks
TS-28 and Mineral Spirits 135	30 to 40 min	1 to 2 months

(4) MODIFICATIONS FOR SPECIAL APPLICATION AND EFFECTS/TRICKS OF THE TRADE

(a) Before applying an overall coating, varnish can be brushed or buffed on locally at leached, absorbent areas where sinking in of the varnish is anticipated. This will help provide an even, uniform appearance when the final varnish coat is applied.

(b) Matte Varnish: Whether brushing or spraying, the key is to keep the varnish layer as thin as possible and to apply it as evenly as possible. Excess varnish can be removed from a brush coat, and the gloss of the coat reduced at the same time, by going over the surface with a dry brush or by rubbing the surface with a piece of velvet or silk cloth wrapped around a wad of cotton. When spraying the varnish, factors that can be varied to produce a matte surface include the speed and power of the spray, droplet size, and spraying distance.

(c) A method to create a matte finish has been reported by one conservator who applies damar 10% in xylene, using silk fabric stuffed with cotton, rubbing the varnish on in a manner similar to French polishing (Ruzga, studio notes). Another approach is to rub down a just-set surface with a fine sponge or silk pad with controlled amounts of deionized water (Bernstein 1992, 117). These buffing techniques are recommended with caution.

(d) The addition of a limited amount of purified beeswax to matte down a damar varnish was readily used in the past. The wax was either added to the damar solution prior to a final varnish application or over a dried final varnish coating. If this technique is needed as an option for a final varnish adjustments, it is recommended that the conservator use a microcrystalline wax and test various prepared dilutions prior to application. The addition of wax in a varnish or as a final buffed layer will make the outer varnish layer more vulnerable to airborne pollutants. (For a dated wax varnish polish recipe and good application technique, see Plenderleith and Werner 1971, 184–5; for a dated matte varnish recipe, see Doerner 1962, 210.)

(e) Some conservators buff fine damar dust, alumina, or silica compounds over a hardened coat of damar to matte down the surface. This treatment can be very successful on paintings with flat surfaces. It can also be used locally on areas where unusual surface varnish anomalies have occurred or in areas of overly glossy inpainting. (For an excellent description of how to apply fine abrasive compounds, see Bernstein 1992, 117.)

(f) For the addition of light stabilizers, see Section VII.,A., Phenolic Antioxidants, Stabilizers, and UV Absorbers.

Aging Characteristics

(1) CHEMICAL PROCESS

The primary process of deterioration of damar is autoxidation (Feller, Stolow, and Jones 1985, 155). The primary initiates for autoxidation are photochemical (especially in the near ultraviolet range) and thermal energies (Mills and White 1987, 134). The three main sites where photochemical oxidation is known to occur are at the double carbon bonds, at the carbonyl groups, and at the tertiary hydrogen groups (Thomson 1963, 176). The autoxidation can be accelerated by the presence of ozone, hydrogen peroxide, chlorine, sulfur dioxide, and other gases (Feller et al. 1985, 155). Yellowing results from secondary reactions among autoxidation products and is a thermal nonoxidative process (de la Rie 1988b, 53). Discoloration may occur if less refined grades of solvents are used (Feller et al. 1985, 155).

(2) RESULTANT CHEMICAL AND/OR PHYSICAL ALTERATIONS

The aged damar molecular composition is thought to be more polar with a low molecular weight. Therefore, it remains in a non-crosslinked, low molecular weight form, enabling it to be removed with maximum polar solvents such as ketones and alcohols (Mills and White 1987, 93).

Aged damar films show physical alterations readily seen in visible light: crazing cracking, interlayer cleavage, flaking, embrittlement, loss of gloss, oxidation, and blooming. Bloom is a white haze created when a newly applied varnish coating dries under conditions of extreme humidity and fluctuations in combination with moderate amounts of atmospheric sulfurous gases and ammonium. The whitish material is crystalline ammonium sulfate found in and on the varnish coating (Brommelle 1956, 181). Lastly, due to damar's brittle nature an aged varnish coat can be easily scratched or abraded.

In long-wave ultraviolet light an aged damar film will produce an increasing light yellow/green to bright yellow/blue-green fluorescence.

(3) IMPACT OF AGING UPON

(a) Visual Appearance

Increased yellowing

Diminished clarity from crazing, cracking, or blooming

(b) Solubility and Removability

Aged damar will become more polar and less soluble; however it does not crosslink. Insolubility is thought to increase to a solvent mixture plateau of 50% toluene/50% acetone (Feller et al. 1985, 121).

(4) ATTRACTION AND RETENTION OF DIRT AND GRIME

Because of its relatively high molecular weight, a dried film of damar does not tend to attract and retain dirt. However, due to its slow drying properties, a newly applied varnish should be stored in a dust-free environment.

(5) THEORETICAL LIFETIME

The lifetime of damar is heavily dependent on the environmental conditions in which it is kept and upon the thickness of the film. Commonly discoloration or changes are noted in 25–50 years.

Damar with Tinuvin® 292 in an ultraviolet free environment is predicted to last without color changes for 50 to 100 years.

Health and Safety

Note: The following is a summary made directly from the Material Safety Data Sheet (MSDS) for damar. Some of the recommendations from the MSDS suggest that conservators use damar at a heated temperature and therefore should protect themselves from molten wax. It is expected that all conservators know that damar in solution should not be heated due to the high risk of explosion and fire. It is not the place for this conservator to alter the information made available on the MSDS. However, in portions of this section that recommend emergency first aid against heated products, consider instead the solvents you are using and read their Material Safety Data Sheet.

(1) EYES

Molten wax, fumes, and/or dust may be irritating to eyes. If hot product is splashed into eyes, flush immediately and thoroughly with clear water and obtain medical attention immediately. Dust may cause mechanical irritation.

(2) INHALATION

Powder grades present hazard as nuisance dust. If overcome by fumes immediately leave the exposure area and obtain medical attention. If breathing is irregular or stops start resuscitation.

(3) DERMAL

Molten wax will cause burning on contact with skin. If burned by hot product obtain medical attention immediately. In case of skin contact with product under other conditions wash thoroughly with soap and water. If discomfort persists obtain medical attention.

(4) INGESTION

No data known or established on acute toxicity by ingestion. No specific information identified or established. If discomfort persists obtain medical attention.

(5) SPECIAL PROTECTION

Eyes: Wear NIOSH Approved goggles or face shield

Ventilation Requirements: Provide adequate ventilation. Always maintain exposure below permissible exposure limits of the diluent

Gloves: Use chemically resistant gloves to avoid contact with skin

Other: Wear chemically resistant gloves with thermal protection and appropriate protective garments when working with molten or hot materials.

Disposal (summarized from MSDS Data sheet)

Waste Disposal: Disposal or incineration must be in compliance with Federal, State, and Local disposal and discharge laws and regulations.

Spill and Leak Procedure: Contain spill and recover material. Advise EPA, State, and Local agency if required.

Ketone Resin Varnishes

Laropal® K80

[cyclohexanone polycondensation resin]

Historical Background

Laropal® K80 was introduced by BASF in 1979. Its marketing has been directed at the printing and paint industries. Laropal® K80 is a “pale, nonhydrolyzable ketone resin for alkyd resin paints and cellulose nitrate lacquers and for use in combination with nonhydrolyzable binders. Its main function is to improve build, gloss and hardness.” (BASF Technical Information Sheet July, 1995). It was not developed as a film forming coating, but as an additive for alkyd resin paints, cellulose nitrate lacquers, vinyl chloride copolymer paints, and chlorinated rubber paints. It has been used as a additive in wood finishing and in the paint industry specifically as a paint grinding aid (Glass-BASF, unpublished).

Source

Laropal® K80 is a polycyclohexanone condensation resin. According to Mills and White, “cyclohexanone can be converted to a low weight polymer by treatment with a methanolic alkali either alone or in the presence of added formaldehyde through an aldol condensation reaction. [These authors believe formaldehyde was not used in manufacturing products used by conservators; however, they did not say how they reached this conclusion.] The ketones and alcohols produced by the aldol condensation can then undergo hydrogen exchange in the presence of alkali, by the ketone oxidizing the alcohol. If formaldehyde is added it can react with cyclohexanone followed by condensation” (Mills and White 1987, 118). To understand how Laropal® K80 fits the technical development of polycyclohexanone condensation resins, the history of their development should be reviewed.

Two major companies have historically produced cyclohexanone resins: BASF in Germany and Howard's of Ilford in England. BASF's first cyclohexanone resin was actually a mixture of cyclohexanones and methyl cyclohexanones called AW2®. AW2® was patented by BASF in 1930. This was replaced by Ketone Resin N® in 1960. Ketone Resin N® was a polycondensation product derived from cyclohexanone alone, but was highly susceptible to light-induced oxidation. Laropal® K80 is the most recent polycyclohexanone condensation resin manufactured by BASF. In the marketing literature it is called the “new” version of Ketone Resin N®. It is light stable, and nonhydrolyzable. De la Rie and Shedrinsky found in their research that Ketone Resin N® and Laropal® K80 have identical characteristics when analyzed. The difference between the two resins occurs in the manufacturing process (Stanger-BASF, unpublished). Ketone Resin N® was manufactured in a discontinuous process and Laropal® K80 is manufactured in a continuous process. Subtle differences which may exist between the resins, due to the process changes, have not been identifiable through analysis of the final product by these scientists (de la Rie and Shedrinsky 1989).

Manufacturers and Vendors

Laropal® K80 is available from Conservator's Emporium (See Appendix II, Vendor Directory).

Chemical and Physical Properties

(The following information is from the Technical Information Data Sheet on Laropal® K80 from BASF, revised July, 1995, unless otherwise noted.)

(1) CHEMICAL CLASSIFICATION

Cyclohexanone polycondensation resin

(2) CHEMICAL STRUCTURE

The precise structure of Laropal® K80 is proprietary information. The following is a theoretical model of a cyclohexanone polycondensation resin (Mills and White 1987, 119).

(3) MOLECULAR WEIGHTS

Maximum Mw: 693 (grams per mole)

average Mw: 426 (grams per mole)

(4) REFRACTIVE INDEX: 1.529

(de la Rie 1990, 168).

(5) SOLUBILITY

Shell Odorless Mineral Spirits/Shell Sol® 71	PIG
Stoddard Solvent/Shell Sol® 340 H	S
Shell Mineral Spirits 145	S
Petroleum Benzine	S
Turpentine	S
Shell Cyclo Sol® 100/Shell Cyclo Sol® 53	S

Xylenes	S
Toluene	S
Isopropanol	S
Ethanol	S*
Acetone	SC
Arcosolv® PM/1-Methoxy-2-propanol	S
* yellow

Terms

S	Soluble	clear solution
SC	Soluble Cloudy	completely dissolved, slightly cloudy solution
SV	Soluble Viscous	clear, highly viscous solution
SR	Soluble Residue	residue on the bottom
PSG	Partially Soluble Gel	resin is dissolved in a clear soft gel in a two-phase mixture with solvent on top
PIG	Partially Soluble Immobile Gel	resin is dissolved in a hard gel in a two-phase mixture with solvent on top
IM	Insoluble Milky	insoluble but a minute fraction has swollen and whitened, solvent looks milky
IC	Insoluble Clear	insoluble but a small portion of the resin has swollen to the point that it is stuck to the bottom of the jar, solvent is clear
I	Insoluble	insoluble, undissolved resin sits in clear solvent

Examples: S to PSG = mostly soluble; PIG to I = mostly insoluble

See also Appendix I, Solubility Testing Description and Solvents Used in Testing.

(6) GLASS TRANSITION TEMPERATURE

75°–85°C

(7) BRITTLENESS AND FLEXIBILITY

Not tested as a film by BASF.

Preparation/Formulation

(1) TYPICAL BRUSH SOLUTIONS

The resin can be brushed effectively in solutions between 10% and 30% (weight to volume). It can be readily dissolved in refined mineral spirits (best available at hardware stores; % aromatics not known) (Ventresco 1995). A recipe given by the CCI Varnish Workshop suggested 45.0 g of Laropal® K80 to 300.0 ml of mineral spirits with 18% aromatics (Carlyle and Bourdeau 1994). To put the Laropal® into solution, the resin can be suspended in a cheesecloth bag in a jar of measured solvent. The resin will go into solution in several days. To speed up the solvation, either add a more polar solvent or gently warm the solution and stir.

(2) TYPICAL SPRAY SOLUTIONS

The resin can be effectively sprayed in solutions between 10% and 30% (weight to volume) (Ventresco 1995). The CCI Varnish Workshop provided two recipes: a) 10–15% (weight to volume) in mineral/white spirits (18% aromatics); or b) 10% (weight to volume) in a 60:40 solution mineral/white spirits (15–20% aromatics):xylenes plus microcrystalline wax, e.g., Cosmolloid® 80-H - Picreator (quantity depends on degree of matteness sought) (Carlyle and Bourdeau 1994).

(3) ADDITIVES

Modification of the visual characteristics of Laropal® K80 can be made by changes in the handling technique or the addition of matting agents such as microcrystalline wax.

Research reports that no additives thus far tested significantly inhibit the autoxidative degradation of Laropal® K80 (Lafontaine 1978, 8–12; de la Rie 1990, 168). However, see following section f), Aging Characteristics, for mention of a 1995 report that contradicts these findings.

(4) STORAGE/SHELF LIFE

The shelf life of Laropal® K80 is two years at temperatures of 40°C or less (BASF Technical Information Data Sheet July, 1995).

Working Characteristics and Practical Properties

Cyclohexanone resins have long been used by conservators because of their excellent visual characteristics and workability. Laropal® K80 resin has a low molecular weight, low viscosity, and saturates colors beautifully (Burke 1984). It is soluble in relatively “mild” solvents as listed above under d)(5).

Laropal® K80 has also been used at a 10% concentration (diluted weight to volume in highly refined mineral spirits) for both brush and spray coats by Barbara Ventresco (Ventresco 1995), who has found that it saturates the paint film very well and can be worked for several minutes to achieve an even, thin coating. The painting is then left to dry overnight before any further work is done. If the surface appears too glossy after drying, a very small amount of powdered resin can be rubbed onto the surface with the fingertips. The surface can then be sprayed or brushed with a solvent to resaturate the film, and it will dry to a softer finish. This technique can be used locally to adjust the surface gloss. The resin can be sprayed to increase both saturation and modify surface characteristics. Ventresco generally uses the varnish between layers of Paraloid® B-72 to improve the B-72's poor paint saturation. As mentioned above, wax can be added to the Laropal® to modify surface gloss. One note of caution: Do not try to dilute the resin with Stoddard Solvent once it is dissolved. The resin will drop out of solution.

Aging Characteristics

Laropal® K80 contains a large number of ketone groups and is susceptible to Norrish type cleavage reactions. As a result of degradation, ketone resin coatings rapidly lose solubility in nonpolar solvents, develop matte spots, and embrittle (de la Rie and Shedrinsky 1989, 9). To date, an additive has not been found that can permanently stabilize Laropal® K80. For example, research on the antioxidant Irganox® by Lafontaine in the 1970s and de la Rie in the 1980s showed that Irganox® 565 did not effectively stabilize Laropal® K80 (Lafontaine 1978, 11; de la Rie 1988, 109–14). De la Rie further found that the hindered amine light stabilizer Tinuvin® 292 did not significantly inhibit autoxidative degradation of Laropal® K80 (de la Rie and McGlinchey 1990, 168). Without modification, Laropal® K80 yellows less than damar, but is prone to the aging problems mentioned above (de la Rie 1991, 74).

Another issue is the resin's brittleness. BASF found that, as a film-forming resin, Laropal® K80 was uselessly brittle. Practicing conservators have not mentioned this as an overwhelming problem; however, it has been used in conjunction with other resin layers (Ventresco 1995; Burke 1984). This resin is not excessively prone to attract dirt and grime (Ventresco 1995). However, in III.D.5.b), The History of Synthetic Resin Varnishes, Bradford Epley mentions a 1995 report by Jerzy Ciabach describing the addition of methacrylates of low polymerization (Plexigum® P28 or Plexigum® PQ610) and Sanduvor® 3050 (hindered amine light stabilizer) to Laropal® K80 resulting in Laropal® K80 films exhibiting increased flexibility, improved resistance to light, and improved solubility upon aging (Ciabach 1995, 186).

Health and Safety (BASF, 1986)

(1) SAFETY

Flash Point: N/A for dry resin

Extinguishing Medium: use water fog, alcohol foam, or dry chemical extinguishing media Special Firefighting Procedures: self-contained breathing apparatus and turn out gear Unusual Fire and Explosion Hazards: Adequate ventilation and clean-up must be maintained to minimize dust accumulation. May form explosive dust-air mixture.

(2) HEALTH

Effects of Overexposure: Contact with eyes or skin may result in temporary mechanical irritation. Repeated to prolonged contact may cause sensitization in susceptible individuals. Ingestion may result in gastric disturbances. Inhalation of dust may irritate the respiratory tract.

First Aid Procedures:

(a) Eyes - Immediately wash eyes with running water for 15 minutes. If irritation develops, consult a physician.

(b) Skin - Wash affected areas with soap and water. Remove and launder contaminated clothing before reuse. If irritation develops, consult a physician.

(c) Ingestion - If swallowed, dilute with water and immediately induce vomiting. Never give fluids or induce vomiting if the victim is unconscious or having convulsions. Get immediate medical attention.

(d) Inhalation - Move to fresh air. Aid in breathing, if necessary, and get immediate medical attention.

(3) SPECIAL PROTECTION

Respiratory Protection: NIOSH/MSHA approved dust respirator as necessary.

Eye Protection: Chemical goggles.

Protective Clothing: Gloves and protective clothing as necessary to minimize skin contact.

Ventilation: Use local exhaust to control dusts.

Disposal

Dispose of in a licensed facility. Recommended crushing or other means to prevent unauthorized reuses.

MS2A®

[A chemically reduced cyclic ketone resin prepared by the polycondensation reaction between methylcyclohexanone and alkaline alcohol (resulting in MS2®, methyl sestone), followed by a chemical reduction]

Historical Background

(1) INDUSTRIAL USE

MS2A® has always been produced and marketed exclusively for conservation purposes. The spelling in the earliest literature is MS-2A® (Thomson 1963; Feller 1963) but Lank uses MS2A® as early as 1972 (Lank 1976). The two spellings are both used in the 1970s and 1980s but MS2A® predominates in writings from the late 1980s onward, notably in de la Rie, 1989–93.

(2) CONSERVATION USE

MS2A® was first developed in the late 1950s at the suggestion of Garry Thomson (Scientific Advisor at The National Gallery, London) following research to improve the ketone resins of the period, MS2® and AW2® (de la Rie, 1989, 12). Since its introduction, it has been used primarily in Great Britain in the larger museums and by private restorers. Until recently, its use in other countries is generally traceable to a British connection. The difficulty of obtaining MS2A® as well as its expense have curtailed its widespread use. MS2A® was out of production from the late 1960s to the early 1980s, and in the 1980s was produced only in small quantities. In 1993 its production was taken over by Linden Chemicals (now Linden Nazareth), resulting in greater availability (from conversations with North American and British conservators; Carlyle and Bourdeau 1994, 53).

Source

(1) PHYSICAL FORM

A pale yellow resin produced in small granule form (Linden Nazareth).

(2) ORIGIN AND MANUFACTURE

A chemically reduced ketone resin, first developed from the ketone resin MS2® in the late 1950s by Howards of Ilford, the producers of MS2®, following input and research by the National Gallery of London (Thomson, 1963; Linden Nazareth). In 1963 Howards changed the manufacturing process of MS2®, rendering it no longer suitable as the basis for MS2A®. Howards then replaced MS2A® with MS2B® which was obtained by the reduction of the German BASF ketone resin AW2®. In 1967 the production of MS2B® stopped when BASF replaced AW2® with Ketone Resin® N. These changes “were initiated by chemical differences between the starting materials: MS2 produced after 1963 as well as Ketone Resin N reportedly gave uselessly brittle products after reduction,” probably due to “the fact that ‘new’ MS2 and Ketone Resin N were condensation products of cyclohexanone only, rather than of a mixture of cyclohexanone and methylcyclohexanones” (de la Rie and Shedrinsky 1989, 13). “When Howards of Ilford was incorporated into the Laporte Group in the late 1960s, MS2A did not fit any product portfolio and was no longer commercially developed … But continuing demand from conservators led Laporte to recommence its production on a limited scale in its Research and Development Pilot Plant at Widnes in Cheshire beginning in 1982. This was continued until 1992 when control of the pilot facility at Widnes was transferred away from Laporte.” In late 1993 Linden Chemicals (now Linden Nazareth) took over the production of MS2A® (Crombie 1994, 43).

(3) MANUFACTURERS AND VENDORS

Available solely from: Linden Nazareth, Hendre Wen, Nazareth, Caenardon, Gwynedd LL54 6DU, Wales, U.K.;Tel. 01286 882162, Fax: 01286 882286. It is packaged in polypropylene tubs containing 0.5 kg of MS2A® and the cost [December, 1997] is $585 per kg (Linden Nazareth).

Chemical and Physical Properties

(1) CHEMICAL CLASSIFICATION

MS2A® is a chemically reduced, cyclic ketone resin prepared by the polycondensation reaction between methylcyclohexanone and alkaline alcohol (resulting in MS2®, methyl sestone) followed by a chemical reduction. In the reduction process, the carbonyl groups are reduced to hydroxy groups using sodium borohydride. The chemical reduction stage removes unsaturation and ketone functions (de la Rie and Shedrinsky 1989, 12).

(2) CHEMICAL FORMULATION/STRUCTURE

First, the reaction creating MS2® can be shown as follows:

In practice a 1000-molecular-weight unit contains a low ketone and high hydroxyl content, suggesting a significant involvement of the step 1 reaction product, together with accompanying methylization reactions of the type:

Subsequent hydrogenation of MS2® to MS2A® removes color-forming bodies converting ketone groups to OH and removing unsaturation (Linden Nazareth).

(3) MOLECULAR WEIGHTS

Weight average molecular weight - 1776 g/mol

Number average molecular weight - 769 g/mol

Polydispersity = 1776/769 = 2.31

(Measurements, kindly supplied by Vincent Routledge of Linden Nazareth, are from batch 15021, prepared in January, 1995. G.P.C. data have been calculated against polystyrene standards for the individual components of the trace, and of the trace as a whole. The polydispersity determination was carried out using Millipore's MAXIMA (c) 820 GPC Analysis Report using 74 slices of five-second widths from 13.97 mins to 20.13 mins.)

(4) REFRACTIVE INDEX 1.505 (LINDEN NAZARETH)

(5) SOLUBILITY

Shell Odorless Mineral Spirits/Shell Sol® 71	S
Stoddard Solvent/Shell Sol® 340 HT	S
Shell Mineral Spirits 145	S
Petroleum Benzine	S
Turpentine	S
Shell Cyclo Sol® 100/Shell Cyclo Sol® 53	S

Xylenes	S
Toluene	S
Isopropanol	S
Ethanol	SR
Acetone	IC
Arcosolv® PM/1-Methoxy-2-propanol	S

Terms

S	Soluble	clear solution
SC	Soluble Cloudy	completely dissolved, slightly cloudy solution
SV	Soluble Viscous	clear, highly viscous solution
SR	Soluble Residue	residue on the bottom
PSG	Partially Soluble Gel	resin is dissolved in a clear soft gel in a two-phase mixture with solvent on top
PIG	Partially Soluble Immobile Gel	resin is dissolved in a hard gel in a two-phase mixture with solvent on top
IM	Insoluble Milky	insoluble but a minute fraction has swollen and whitened, solvent looks milky
IC	Insoluble Clear	insoluble but a small portion of the resin has swollen to the point that it is stuck to the bottom of the jar, solvent is clear
I	Insoluble	insoluble, undissolved resin sits in clear solvent

Examples: S to PSG = mostly soluble; PIG to I = mostly insoluble

See also Appendix I, Solubility Testing Description and Solvents Used in Testing.

(6) GLASS TRANSITION TEMPERATURE

57°C (de la Rie and Shedrinsky 1989, 14).

(7) BRITTLENESS AND FLEXIBILITY

The resin is quite brittle: Yield point - not available Break point - 189 (From testing in which a coating of the resin was applied to a metallic plate. The value is the radius in mm of the circle which fits the bend at which cracking starts to occur. “Standardized flexibility tests such as ASTM D 522 are unsuitable” [[[#ref82|de la Rie and Shedrinsky 1989]], 14].)

(8) HARDNESS

Pendulum hardness value = 214;“Koenig pendulum hardness values were determined on a Byk-Chemie pendulum hardness tester according to ASTM method D 4366” (de la Rie and Shedrinsky 1989, 17).

Preparation/Formulation

(1) TYPICAL BRUSH SOLUTIONS

(a) 5–20% MS2A® resin weight/volume in Stoddard Solvent

Percentage depends on the working properties and final effect desired. The resin granules are suspended in a porous cloth bag (cheese cloth, nylon stocking, etc.) in the solvent for one to two days, and the batch is stirred occasionally or shaken. Warming in a double boiler speeds up the process to 1/2–1 hour duration but is not necessary (National Gallery of Art, Washington).

(b) 500 g MS2A®

1.25 1 odorless mineral spirits, i.e., white spirit with low aromatic content. (125 ml n-butyl acetate—no longer recommended by Lank, see 3.b) below)

“It is preferable to grind the polymer finely since larger pieces of MS2A take a very long time indeed to dissolve in odorless mineral spirits” (Carlyle and Bourdeau 1994, 53, adaptation of the first recipes published for the use of MS2A® by H. Lank at the Lisbon IIC conference in 1972 - see (3) below). The manufacturer has said that any batch of MS2A® which will not dissolve properly in white spirit should be returned (Woudhuysen-Keller 1995). (Ed. Note:This recipe makes a very large batch which would require long storage, not recommended in recent literature.)

(2) TYPICAL SPRAY SOLUTIONS

(a) 5–15% MS2A® weight/volume in Stoddard Solvent depending on working properties desired. Dissolve as under b.1.a) above (National Gallery of Art, Washington).

(b) 30% MS2A® in Mineral Spirits (Carlyle and Bourdeau 1994, 53).

(c) Microcrystalline wax is often added to the final sprayed layer(s) to reduce the brittleness of the varnish, manipulate the gloss, and reduce the “flinty” appearance. Two practices for the addition of wax have been found, one a more precisely measured addition not involving heat, and the other more “intuitive” and often using heat to speed the process. In the latter, conservators add a “pea-to-walnut”-sized piece of microcrystalline wax to the MS2A® varnish in the varnish container of a spray gun which can then be warmed in a double boiler to melt the wax. The solution is gently stirred to disperse the wax thoroughly (National Gallery of Art, Washington). The other, less arbitrary, approach involves the addition of a pre-existing standard matte solution in proportion to the standard solution and is done at room temperature to avoid excess wax in the varnish at higher temperatures (See c)(3)(c) and (4)(a) below; and d)(4), Lank 1996 correspondence).

(d) Matte MS2A® Varnish (Carlyle and Bourdeau, 1994, 53):

30% MS2A® in mineral spirits	270 ml
Cosmolloid 80H wax	60 g
solvent (mineral spirits)	1.3 1

(3) SOLUTIONS RECOMMENDED BY HERBERT LANK, 1972, UPDATED 1996

(This information from the 1972 Lisbon Conference, edited and published in 1976, was kindly updated by Lank in a letter to the contributor in April, 1996. See Lank, 1976 for detailed information.)

(a) Standard Solution (25 – 31% w/v)

500 g MS2A® are dissolved in 1100 ml white spirit (white spirit with high aromatic content will not form a film when sprayed, so add some n-decane to lower the aromatic content). Continuous stirring for 5–6 hours dissolves the resin completely. This solution is designed for spray pressures of 2–5 kg/cm2.

(b) Brushing Varnish

8 parts per vol. standard solution

2 parts per vol. white spirit

(1 part per vol. n-butyl acetate) [Note: 1996 - no longer used]

This is brushed on thinly as an isolating layer.

(c) Matte Varnish for Spray Application

270 ml standard solution

60 gm Cosmolloid® wax 80H

1300 ml white spirit

The wax is melted in a water bath with a little white spirit. The previously warmed bulk of the white spirit is then added, followed by the standard varnish solution (Developed by J. Plesters, National Gallery, London; may be suitable for modern, Impressionist pictures).

(d) Final Varnish

3 parts per vol. standard solution MS2A®

.5 parts per vol. matte varnish (Note: 1972 proportion was 1 part per vol.)

To be sprayed on as final layer on paintings. Good for dulling down an overly glossy varnish. (See d)(4)(a) below for importance of correct formulation.)

(4) ADDITIVES

(a) Microcrystalline wax (See (2)(c) above for initial discussion)

Recent reports suggest that its usage has been curtailed by some to avoid dust attraction and reduced saturation (see e)(3)(c) below). But Lank writes: “We find that dust is not absorbed into the properly formulated and applied final varnish layer. On paintings which have travelled around for several years in multiple exhibitions, there is usually a film of dust and grime … This is removed by washing the surface of the varnish gently with distilled water, drying and then polishing with a soft cloth. This … does not abrade the varnish. The appearance of the paintings which seemed to have lost in saturation, was then found to be virtually unchanged” (Lank 1996).

(b) Tinuvin® 292 hindered amine light stabilizer (HALS)

The addition of 1% (w/w resin) Tinuvin® 292 to a freshly made batch has been shown to stabilize to some extent a film of MS2A® during artificial aging, and it is suggested that a 2% solution would stabilize it significantly more (de la Rie, 1993, 568). Note that stabilization occurs even in the presence of ultraviolet light below 400 nm. Many conservators commonly add 2% Tinuvin® 292 to their MS2A® solutions.

(5) SPECIAL CONSIDERATIONS

(a) Tendency to reticulate

Lank states that if properly made up and applied, this does not occur any more than with other varnishes and should not happen (Lank 1996). Others have had recurring reticulation problems (see c.(3)(d)).

(6) OTHER

(a) De la Rie has recommended making up a fresh batch of varnish for each application, no matter what varnish is being used (verbal communication and National Gallery of Art information sheets). Batches should be stored for no longer than three weeks.

Therefore, it is not good practice for conservators to make up a stock solution of MS2A® and keep it for months.

Working Characteristics and Practical Properties

(1) APPEARANCE

MS2A®'s optical appearance is considered to be one of its greatest advantages: it has a silken gloss and is softer and less shiny than damar. “The consensus among conservators who were surveyed was that MS2A was very expensive; however, many of those who used it felt that it was well worth the price, with praise that it produces one of the most beautiful varnishes” (Carlyle and Bourdeau 1994,53).

MS2A®'s saturation is not as good as damar or the new low molecular weight synthetics but much better than the long-chained polymers. It conforms well to the paint surface, and if properly applied gives a very lively, varied, sensitive appearance to the paint surface (private conversations with conservators).

(2) BRUSHING

(a) Open/Working Time

Depends on the solvent used, but usually of medium length, when Stoddard Solvent is used. Easy to manipulate, it can be worked and reworked with the brush as the solvent evaporates to effect a desired appearance. A rare advantage is that it can be added and reworked locally with small brushes on a pre-existing, “dried” layer of MS2A® to build up the gloss of uneven areas (see (4)(a) below). Lank emphasizes that the applications should be as thin as possible. The purpose of the brush application is solely to facilitate wetting the paint surface: sprayed MS2A® will not “take” on a surface without the preliminary brushed layer unless it contains wax.

(b) Drying Time

Again, depends on the solvent used but usually slow. After brush application, painting can be set vertical quite soon to avoid dust accumulation.

(c) Usual Application

Applied with brush as an isolating layer prior to inpainting and prior to the sprayed final coating. MS2A® is usually applied with a hog's bristle varnish brush, two-three inches wide and thin in cross section. Application methods vary: patterns include rows of rectangles with well feathered edges, the Union Jack pattern in diagonals across the painting, dabs of equal varnish amounts dotted very quickly all across the painting and then joined by fast, feathered brushing, or successive rows applied parallel to and from the painting's short side for two-thirds the length of the painting, then brushed across at right angles into the uncovered area.

Some prefer a very thin isolating layer, which can leave the paint surface quite uneven in appearance. They build up varnish evenness during inpainting, applying the varnish locally to matte areas with a small brush while the painting is on the easel. They achieve enough of the appearance desired with this local brushing to need only a thin final spray layer, often containing a touch of wax. Others prefer a thicker isolating layer so that inpainting is carried out on a more even coating, and again only a thin final spray layer is necessary. Lank emphasizes that “the minimum total amount of the varnish is what is desired…. If the initial brush coat is too thick, the advantage of using MS2A is lost” (Lank 1996).

(3) SPRAYING

(a) Open/Working Time

Depends on formulation, distance from painting, ratio of varnish to air, etc.: with Stoddard Solvent open time is of medium length: can easily be lightly tamped or reworked with soft brush, although normally this is not necessary.

(b) Drying Time

Depends on the same factors as above: with Stoddard Solvent, it is slow. The painting should remain vertical to avoid dust.

(c) Usual Application

Usually applied in the number of layers desired over the brushed isolating layer and over any inpainting present (see e)(2)(c) above). Some conservators interlayer final glazes of inpainting between thin sprayed layers. A small amount of wax is often added to the final layer. Some prefer to add a little wax to several thin final spray layers to effect a desired appearance. However, recently many prefer to achieve the desired matteness and sheen by brush and spray gun manipulation rather than by the addition of wax which can “pick up dust and ruin the saturation” (Woudhuysen-Keller 1995; but note d)(4)(a) above). Lank emphasizes that application is a skill requiring practice and confidence.

(d) Special Considerations When Spraying

Sprayed MS2A® can reticulate very easily, especially when sprayed on panel paintings, although note Lank in b)(5)(a) above. Reticulation has been found to occur commonly while spraying on panel paintings over earlier MS2A® layers but can also occur in the first varnish layer on the paint surface. Attempts to deal with this include waiting up to a week between spray layers and spraying in very thin layers. Varnish formulation changes may help but no one reports this. When reticulation occurs, conservators have successfully corrected it by quickly placing the painting horizontal, face up, and brushing or tamping the reticulated varnish surface quickly overall with a large badger hair brush. This can be successful over inpainting in poly(vinyl acetate) and an MS2A® isolating layer (National Gallery of Art).

(4) MODIFICATIONS FOR SPECIAL APPLICATIONS AND EFFECTS/TRICKS OF THE TRADE

(a) Techniques For Local Varnish Application to Build up Gloss in Matte Areas

This is carried out while the painting is vertical, on the easel, usually during inpainting. An approximately one-inch-wide sable brush can be used; some conservators cut off the bristles to approximately half their length at a slight angle. Keep the brush barely wet by tamping it on a paper towel after dipping it in the varnish (a thick or thin solution, depending on the gloss needed), and brush the MS2A® vigorously into the matte area, feathering the edges, and holding the brush at a slight angle, often working it away from you. Others prefer using large inpainting brushes and evenly applying the varnish in parallel strokes over the matte areas. In both techniques, the new MS2A® blends into the surrounding layer without the formation of edges if properly applied.

(b) Inpainting

Inpainting can be carried out in conjunction with an MS2A® varnishing system in many ways. In one example, the inpainting is in a medium such as poly(vinyl acetate), or is in a medium soluble in “milder” solvents but is protected by a local isolating layer of poly(vinyl acetate). This inpainting is applied over an isolating layer of MS2A® and then covered by final spray coats of MS2A® as needed. In another example, inpainting is in a water-based medium applied over the thin MS2A® isolating layer and locally isolated with varnish; then final inpainting is applied in thin glazes, often in the MS2A® medium, and interlayered with final spray MS2A® layers to achieve the desired effect.

(c) Compound Uses

Over Paraloid® B72 - Some British conservators report using MS2A® as a final layer sprayed over an isolating brush layer of Paraloid® B72 (verbal communication with conservators). Thereby the most stable layer is next to the painting and the more easily manipulated, more “aesthetically pleasing” layer is uppermost.

Over damar - Some conservators report spraying MS2A® over damar as a final surface coating. Thereby the most saturating layer is next to the paint surface and, again, the more “aesthetically pleasing” layer is on the surface.

(5) SPECIAL CONSIDERATIONS

It must be remembered that an MS2A® layer is brittle, susceptible to scratches, abrasion, etc. Take special care in handling, use good frame rabbet protection, be careful not to leave marks when dusting, etc.

Aging Characteristics

(1) CHEMICAL PROCESS

The degradation is an autoxidation process similar to the aging of nonreduced ketones but is slower due to the elimination of ketone groups, the weakest parts of the ketone molecules, in the reduction process. In MS2A®, carbonyl groups have been reduced to hydroxy groups to make it more stable. Other sites in the ketone molecule susceptible to degradation include ether groups, tertiary carbon atoms, and carbon-carbon double bonds (de la Rie 1989, 12–13; Lerner 1991, 94–7).

(2) RESULTANT CHEMICAL/PHYSICAL ALTERATIONS

MS2A® has traditionally been found to be considerably more stable than its parent ketone resins, in that it is more resistant to oxidation and has no serious problems with crosslinking (see Laropal® Section) (Thomson 1963, 183; de la Rie and Shedrinsky 1989, 12–13). Recent work by de la Rie finds that MS2A®'s reduced removability on aging is not significantly different from the unmodified ketones (de la Rie 1993, 568) but this is specifically in comparison with the low molecular weight synthetic resins. As a result of oxidation, “solubility in apolar solvents is rapidly reduced and other defects such as microscopic wrinkling may occur. These oxidized varnishes (ketones) are sensitive to water and may be damaged when condensation occurs due to temperature or RH fluctuations” (de la Rie, correspondence with Lank, 1994). In practice, conservators have not reported such occurrences with MS2A®.

(3) IMPACT OF AGING UPON

(a) Visual Appearance

MS2A® yellows much less than do the natural resins and has been reported by some to be preferred for use in uncontrollable, high-ultraviolet light conditions. Practical experience reports that, to the naked eye, its gloss, clarity and saturation have not changed significantly on numerous treatments from the late 1950s-early 1960s in Great Britain, on paintings hanging usually in favorable conditions. Problems of wrinkling, predicted by Thomson in 1963, have not been observed (private conversations with David Bull, Viola Pemberton-Piggott, Renate Woudhuysen-Keller). Lank reports that the naked eye could detect no discoloration on removal of a 30-year-old MS2A® coating with a swab and white spirit (Lank 1996).

(b) Solubility and Removability

As reported in d)(2) above, recent work by de la Rie suggests removability may be affected by aging more than initially thought. Practical experience reports that 30-year-old coatings are easily removable with white spirit (Lank 1996).

(4) ATTRACTION AND RETENTION OF DIRT AND GRIME

The addition of microcrystalline wax to the final varnish layer can contribute to the attraction and retention of dust (but see b)(4)(a) above). Without wax, no significant attraction has been noted.

(5) THEORETICAL LIFETIME

The conservator may well be uncertain about whether or not MS2A® ages “reliably.” Theoretical evidence is not yet complete: much of the research focuses on the unreduced ketones and the new synthetic low molecular weight resins, and not on MS2A®. De la Rie's research is skeptical about MS2A®'s longevity due to its brittleness and due to his recent tests showing its reduced removability on aging (de la Rie 1993, 568). Much of this research has compared MS2A® with the extremely stable, low molecular weight synthetic resins, which, however, are more difficult to manipulate and sometimes considered less aesthetically pleasing. In practice, 30–37-year old examples of MS2A® on paintings appear unchanged and conservators have reported no removability problems (conversations with British conservators). The brittleness about which all researchers worry may little affect a coating kept in a very stable environment with rare movement but may affect the theoretical lifetime of a less protected coating, producing fine crazing, wrinkling, and pathways for degradation to start.

Health and Safety (Materials Safety Data Sheet)

Flash Point: greater than 105°C

Extinguishing Media: water spray or CO₂

Fire and Explosion Hazards: in a fire, harmful fumes may be emitted

Special Fire Fighting Procedures: in emergency situations self-contained breathing apparatus may be necessary

Hazards Identification: not considered or regulated as a hazardous product under international regulations and codes

Health Hazard Data:

eyes: may cause slight irritation and redness

skin: no significant effects reported

ingestion: may be slightly harmful if swallowed (It was judged that the LD50 oral rate would be greater than 2000 mg/kg after consideration of toxicology for similar products.) inhalation: may be slightly harmful by inhalation

carcenogicity: not known

Emergency and First Aid Procedures:

eyes: immediately and gently irrigate with clean water at least 15 minutes; if irritation develops, contact a physician

skin: remove contaminated clothing; wash affected skin with soap and lots of water; if irritation develops, contact a physician

ingestion: give one pint of milk or water to drink immediately; do not induce vomiting; consult a physician immediately

inhalation: remove to fresh air, keep at rest, consult a physician if symptoms persist

Precautions to Be Taken in Handling and Storage:

Store in sealed containers in cool, dry conditions, with good general ventilation; for handling wear PVC gloves and goggles to prevent mechanical irritation

Exposure Controls (normal use): Wear rubber or PVC gloves, wear goggles to help prevent mechanical irritation; respiratory protection should be worn for applications in solvent-based formulations.

Disposal: For spillage, sweep up carefully (avoid creating airborne dust) and put in lidded plastic containers. Dispose of in accordance with local and national regulations. Not expected to be a significant ecological hazard.

Proprietary Varnishes Based on Ketone Resins

Artists' Gloss Varnish® (formerly Winton®)

Also Artists' Original Matt Varnish®, Artists' Retouching Varnish® (formerly Winton Retouching Varnish®)

Historical Background

Winsor & Newton introduced Winton® in 1950 as a synthetic alternative to damar varnish. It was originally formulated with AW2® resin. In 1967 the formulation was changed to Ketone N®. Since BASF stopped production of Ketone N® in 1979, the ketone resin base probably changed to Laropal® K80, the BASF replacement resin around that time, although this is proprietary information and the manufacturer's representative continued to call the base resin Ketone N®. In 1994, after introducing its new products, Conserv-Art® Gloss and Matt Varnishes, Winsor & Newton changed the name of Winton® to Artists' Gloss Varnish® (Upchurch, 1995).

(1) INDUSTRIAL USE

Ketone resins were developed as additives to increase gloss and hardness in paints and lacquers. They are considered too brittle for use as industrial clear coatings (de la Rie and Shedrinsky 1989, 9). Winsor & Newton's products, Winton®, Artists' Gloss Varnish®, Artists' Original Matt Varnish® and Artists' Retouching Varnish®, all ketone resins, are marketed as varnishes for oil paintings.

(2) CONSERVATION USE

This product has been used by some conservators as an easily available alternative to other ketone resins such as Laropal® K80 and AW2®.

Source

(1) PHYSICAL FORM

The formula for Artists' Gloss Varnish® is 46% cyclohexanone resin (probably Laropal® K80), dissolved in white spirit (Upchurch 1995). Infrared spectra of a bottle of unknown age of Winton® varnish prepared by Winterthur Museum's Analytical Laboratory in 1995 confirmed that the product is a ketone resin such as Ketone N or Laropal® K80. According to BASF, except for the manufacturing process, Ketone Resin N® and Laropal® K80 are identical (de la Rie and Shedrinsky 1989, 10).

(2) ORIGIN AND MANUFACTURE

See Section a) above, “Historical Background.”

(3) MANUFACTURERS AND VENDORS

Artists' Gloss, Original Matt, and Retouching Varnishes are manufactured by Winsor & Newton and distributed by artists' supply stores [see Appendix II, Vendor Directory]. They are available in 75ml, 250 ml, and 500 ml bottles.

The manufacturer's address in the U.S. is: Colart Americas, Inc. Winsor & Newton P.O. Box 1396 Piscataway, N.J. 08855–1396

Chemical and Physical Properties

(1) CHEMICAL CLASSIFICATION

Polycyclohexanone.

(2) CHEMICAL FORMULA/STRUCTURE

The precise structure of Laropal® K80 is proprietary information (Mills and White 1987, 119). See Section IV.C.1., Laropal® K80 for further information.

(3) MOLECULAR WEIGHT

440 (approximate) (Foster 1996)

(4) REFRACTIVE INDEX

1.53 (Foster 1996)

(5) SOLUBILITY

Winton Glossy PV (Retouch)

Shell Odorless Mineral Spirits/Shell Sol® 71	SR
Stoddard Solvent/Shell Sol® 340 HT	S
Shell Mineral Spirits 145	S
Petroleum Benzine	S
Turpentine	S
Shell Cyclo Sol® 100/Shell Cyclo Sol® 53	S

Xylenes	S
Toluene	S
Isopropanol	S
Ethanol	S
Acetone	S
Arcosolv® PM/1-Methoxy-2-propanol	S

Terms

S	Soluble	dear solution
SC	Soluble Cloudy	completely dissolved, slightly cloudy solution
SV	Soluble Viscous	clear, highly viscous solution
SR	Soluble Residue	residue on the bottom
PSG	Partially Soluble Gel	resin is dissolved in a clear soft gel in a two-phase mixture with solvent on top
PIG	Partially Soluble Immobile Gel	resin is dissolved in a hard gel in a two-phase mixture with solvent on top
IM	Insoluble Milky	insoluble but a minute fraction has swollen and whitened, solvent looks milky
IC	Insoluble Clear	insoluble but a small portion of the resin has swollen to the point that it is stuck to the bottom of the jar, solvent is clear
I	Insoluble	insoluble, undissolved resin sits in clear solvent

Examples: S to PSG = mostly soluble; PIG to I = mostly insoluble

See also Appendix I: Solubility Testing Description and Solvents Used in Testing.

(6) GLASS TRANSITION TEMPERATURE

43°C (as reported for Laropal® K80).

Preparation/Formulation

(1) TYPICAL BRUSH SOLUTIONS

The gloss and matte varnishes are sold in the recommended “picture weight” dilution (46% solids) for brush application (Winsor & Newton). Some conservators have used it diluted 1:1 with Stoddard Solvent® or other solvents (Bockrath 1994).

(2) TYPICAL SPRAY SOLUTIONS

The manufacturer recommends further dilution with “mineral spirits” (available at hardware stores) for spray applications (Upchurch 1995).

(3) ADDITIVES

The Artists' Gloss Varnish® contains no additives (Foster 1996). Artists' Original Matt Varnish® contains beeswax as the matting agent and requires warming before use (Upchurch 1995). An earlier Winsor & Newton product, Artists Matt Varnish®, contained silica as the matting agent, as well as an ultraviolet inhibitor. This product was never marketed in the United States (Foster 1996).

(4) SPECIAL CONSIDERATIONS

Because degradation reactions occur faster in solution than in solid form, it is recommended that varnishes be prepared shortly before use and not kept in storage in solution for long periods of time (de la Rie and McGlinchey 1989, 144).

(5) STORAGE/SHELF LIFE

Winsor & Newton claims an indefinite shelf life for these products (Upchurch 1995). BASF, the manufacturer of Laropal® K80 cites a shelf life of two years at temperatures of 40°C or less (BASF, Technical Information Sheet July, 1995).

Working Characteristics and Practical Properties

In general, these products have similar characteristics to Laropal® K80 dissolved in petroleum distillate.

(1) APPEARANCE

The Gloss varnish has a high gloss and good saturation. Gloss and Matt varnishes can be mixed to achieve an intermediate gloss (W&N product label 1996).

(2) BRUSHING

The manufacturer's formula is more concentrated than the 10–30% solutions of ketone resin typically used by conservators. Brushed on, from the bottle, the open time is approximately two minutes. It dries to the touch in two hours. Open time and working properties of a diluted preparation will depend on the concentration and choice of solvent.

(3) SPRAYING

The manufacturer recommends dilution with mineral spirits or Sansodor® Low Odour Paint Thinner (Winsor & Newton) for spray applications.

(4) SPECIAL APPLICATIONS

A thin layer of Winton®, diluted 1:1 with Stoddard Solvent® or petroleum benzine, can be wiped over an initial coat of Paraloid® B-72 to increase saturation and gloss (Bockrath, personal communication 1994). This technique has also been used to improve the surface gloss of aged and dull natural resin varnishes (Samet, personal communication 1995).

Aging Characteristics

Winsor & Newton states that the product is stable for 20–25 years (Upchurch, personal communication 1995). “The solubility of Laropal K80 changes during accelerated aging due to the occurrence of polar oxidation products” (de la Rie and Shredrinsky 1989, 15).

Health and Safety

Hazardous Ingredients: Petroleum distillate

Fire and Explosion Hazard Data:

Flash Point: 41°C (closed cup)

Extinguishing Media: sand, foam, dry powder, water spray

Health Hazard: High concentrations of vapor may be irritating to eyes and respiratory system.

May cause drowsiness, nausea and sickness. Contact with skin may cause irritation.

First Aid:

Eye Contact: Wash with water for 15 minutes.

Skin Contact: Wash off with soap and water.

Inhalation: Remove from exposure

Ingestion: DO NOT INDUCE VOMITING; get medical attention

Control Measures: Avoid contact with skin and eyes. Ensure good ventilation. Wear mask if spraying.

(Winsor & Newton 1994)

Disposal

Store in closed containers away from heat. Dispose as flammable waste in airtight containers (Winsor & Newton 1994).

Talens Picture Varnish® (formerly Rembrandt®)

[based on polycyclohexanone resin Laropal® K80]

Historical Background

(1) INDUSTRIAL USE/ARTISTIC USE

The Talens Rembrandt® line of varnishes was originally produced and marketed for artists' and possibly conservators' use (see 2. below). According to research by Jan Slief of the Research and Development Division of Royal Talens B.V., the Rembrandt Picture Varnish® name was introduced for a varnish with a synthetic, ketone resin as its base, and was never associated with another type of resin. The varnish was first commercially available around 1930, and a US pricelist from Talens dated 1931 already advertises both Rembrandt Picture Varnish® and Rembrandt Retouching Varnish®. The matte varnish was introduced commercially in 1960–61. In 1994 the name Rembrandt was dropped from the line of varnishes and media (personal communication from Jan Slief 1995–96).

(2) CONSERVATION USE

In the 1931 US price list, mentioned above, is the advertisement: “The following is a report of Dr. A.M. DeWild, of the Hague, one of the best restorers of paintings in Holland … ‘For the last six months I have conducted several experiments with the Rembrandt Picture Varnish. I have exposed it to different degrees of humidity, to the effects of sulphur dioxide, to ultraviolet rays and to alternating high and low temperatures, and I am pleased to report that your Rembrandt Picture Varnish is far superior to any Mastic”’ (communication from Jan Slief with photocopy of 1931 US price list). This suggests that, from its earliest production, the varnish was being developed for qualities of major importance to the conservation field, as well as to artists. Jan Slief also sent information from Talens' files on the 1935 varnishing with Rembrandt varnish of Jan van Eyck's Madonna of Canon van der Paele during its conservation treatment by Vanderveken and Phillipot in Brussels, an early example of its use on a specific, well known painting.

Discussion with American and European conservators for this entry suggested that, at present in the United States, the most widespread conservation use of the Talens Picture Varnish® line is among private conservators in New York City and conservators who have been trained by or have worked with them. An incomplete list of conservators who use or have used the varnish includes: Gertrude Blumel, Marco Grassi, Mario and Dianne Dwyer Modestini, Steven Prins, William Suhr, and Frank Zuccari (from conversations with some of these US conservators). Among continental European conservators, Talens picture varnishes are said to be the most frequently used of all the proprietary varnishes. In Canada and Britain there is less use of proprietary varnishes, but the use of the Talens line was reported among some private conservators in Canada (Carlyle and Bourdeau 1994, 55).

Source

(1) PHYSICAL FORM

(a) (Rembrandt®) Picture Varnish-Glossy - a clear solution of Laropal® K80 ketone resin in White Spirit and turpentine with plasticizer (castor oil), sold in bottles of different sizes. (Note that the spray can version contains no turpentine, and instead is formulated with White Spirit with a small amount of isopropanol. The propellant is a butane/propane mixture.)

(b) (Rembrandt®) Picture Varnish-Mat - a solution of ketone resin Laropal® K80 in turpentine only, with the addition of wax-based matting agents (beeswax and a synthetic wax). (Note:The same formulation differences as in (a) for spray can version. In the spray can matte varnish, the matting agent is silica, not wax.)

(c) (Rembrandt®) Retouching Varnish - a clear solution of ketone resin Laropal® K80 in mostly White Spirit, with the addition of a small amount of turpentine (mainly for the smell) and approximately 4% (of the total product) isopropanol. (Again, in the spray can version, there is no turpentine.) (Slief, J., Personal communication August, 1996)

(2) ORIGIN AND MANUFACTURE

The three Talens varnish products most commonly used by conservators are: (Rembrandt®) Picture Varnish-Glossy, (Rembrandt®) Picture Varnish-Mat, and (Rembrandt®) Retouching Varnish. They will be referred to herein without the Rembrandt® name which was dropped from the varnish line in 1994. All three have been supplied in bottles in the following sizes: 75 ml, 250 ml, 500 ml, 1000 ml, and a 400 ml spray can. The spray can version will be only briefly mentioned in this section (see Chemical Formulation) as it is rarely used by conservators.

The Talens Company was founded in Holland in 1899 by Mr. Marten Talens, a retired banker. The Rembrandt® line was first started in 1904 with the production of Rembrandt® oil colors. A US branch office was first opened in 1906 by the son of the company's founder. In 1931, the US distribution company was in Irvington, New Jersey. The Dutch factory was bombed in World War II and practically had to start over again in 1945. The company opened several European offices at that time, being very dependent on the international market outside the small Dutch market. A recent history of the company in the United States includes the following: in 1972 the Morilla Co. was the company's US agent. Since 1986 it is a joint venture of Royal Talens and Canson (a French paper company). Meanwhile, the name has been changed to Canson-Talens (Zora Pinney Archives, National Gallery of Art - information from Mr. John Hoogvliet, Chief Chemist [no date, probably 1980s]; research by Paula Volent, 1995 for the National Gallery of Art Modern Materials Collection; communication from Jan Slief, August, 1996).

Historical information on contents:

The Ketone Resin Base: The original resin was AW2®, mentioned in Talens laboratory formula books by 1929. From 1943 to 1947 no varnishes were produced. From 1947 to 1949 the British-produced (Howard's of Ilford) ketone resin MS2® was used but production formulations from 1949 on continue to include AW2®. In 1966–67, when BASF had stopped production of AW2®, BASF's Ketone Resin N® was used, the name of which was changed to Laropal® K80 in 1979.

Solvents: For the Picture Varnish-Glossy, turpentine was always the main solvent; old lab books showed some research on other solvents in the 1930s, for example small amounts of butyl lactate, but since the 40s the majority turpentine/White Spirit mixture has been used. For the Retouching Varnish, the main solvent component has always been White Spirit. Thirty years ago it was a combination of “Special Boiling Point Spirit” with White Spirit. For the last 15 years, the solvent mixture has been the same as described under b)(1)(c) above. The solvent for Picture Varnish-Mat has always remained turpentine alone, because of the solubility of the waxes.

Plasticizers: Castor oil has always been an ingredient of Picture Varnish-Glossy from the beginning. Castor oil is described in the Merck Index as obtained by cold-pressing the seeds of Ricinus communis L., Euphorbiaceae, and as the “starting raw material for many basic industrial chemicals: … a basic ingredient in the production of synthetic resins” (Merck Index 1976,242). Picture Varnish-Mat never contained castor oil because the wax matting agents give it adequate flexibility (Slief, J., Personal communication 1995–96).

(3) MANUFACTURERS AND VENDORS

The manufacturer is Royal Talens, B.V., P.O. Box 4, Sophielaan 46,7300 AA Apeldoorn, Netherlands, Research and Development Department, tel. 31–55–5274700, fax. 31–55–5215286. The U.S. distributor is Canson-Talens, Inc., P.O. Box 220, South Hadley, MA. 01075, tel. (413) 538–9250.

Vendors: Available at certain artists' supply stores, including Pearl Paint Co. in Manhattan and Pearl Paint Co., Rockville, MD. [See Appendix II, Vendor Directory.] Some conservators in New York City have said that it has recently been harder to find the large bottles.

Chemical and Physical Properties

(1) CHEMICAL CLASSIFICATION

The precise contents of the Talens Picture Varnishes are proprietary information. The resin base for all three is the polycyclohexanone resin, Laropal® K80. The Picture Varnish-Glossy includes, but is not necessarily limited to, the solvents turpentine (the major solvent) and White Spirit, and a plasticizer, castor oil. The Picture Varnish-Mat includes turpentine, the only solvent, and wax-based matting agents (beeswax and synthetic waxes). The Retouching Varnish includes as solvent mostly White Spirit, some turpentine, and, 4% of the total, isopropanol (Slief, J., Personal communication 1995–96). Analysis of these products was carried out by Joe Swider and Suzanne Lomax of the Scientific Research Department of the National Gallery of Art. The manufacturer's description of the varnish components was confirmed although the wax in the mat varnish could not be completely characterized (Lomax 1996).

(2) CHEMICAL FORMULATION/STRUCTURE

The chemical formulation and structure of the Laropal® K80 base of the Talens Picture Varnishes can be found in Section IV.C.1., Laropal® K80.

(3) MOLECULAR WEIGHTS

Unknown for the dried films; see Laropal® K80 entry.

(4) REFRACTIVE INDEX

See Laropal K80® entry.

(5) SOLUBILITY

Talens PV Glossy

Shell Odorless Mineral Spirits/Shell Sol® 71	I
Stoddard Solvent/Shell Sol® 340 HT	S
Shell Mineral Spirits 145	S
Petroleum Benzine	S
Turpentine	S
Shell Cyclo Sol® 100/Shell Cyclo Sol® 53	S

Xylenes	S
Toluene	S
Isopropanol	S
Ethanol	S
Acetone	S
Arcosolv® PM/1-Methoxy-2-propanol	S

Terms

S	Soluble	clear solution
SC	Soluble Cloudy	completely dissolved, slightly cloudy solution
SV	Soluble Viscous	clear, highly viscous solution
SR	Soluble Residue	residue on the bottom
PSG	Partially Soluble Gel	resin is dissolved in a dear soft gel in a two-phase mixture with solvent on top
PIG	Partially Soluble Immobile Gel	resin is dissolved in a hard gel in a two-phase mixture with solvent on top
IM	Insoluble Milky	insoluble but a minute fraction has swollen and whitened, solvent looks milky
IC	Insoluble Clear	insoluble but a small portion of the resin has swollen to the point that it is stuck to the bottom of the jar, solvent is clear
I	Insoluble	insoluble, undissolved resin sits in clear solvent

Examples: S to PSG = mostly soluble; PIG to I = mostly insoluble

See also Appendix I, Solubility Testing Description and Solvents Used in Testing.

(6) GLASS TRANSITION TEMPERATURE

Not available. See Laropal® K80 entry.

Preparation/Formulation

(1) TYPICAL BRUSH SOLUTIONS

(a) Picture Varnish-Glossy

Used undiluted or thinned with turpentine or mineral spirits (Stoddard Solvent®, White Spirit, etc).

(b) Retouching Varnish

Used undiluted or with the addition of turpentine or a small amount of mineral spirits (too much mineral spirits causes the varnish to get cloudy and go out of solution). Many conservators prefer using this varnish over the other Talens varnishes because it has fewer additives. However most conservators have a problem with its thinness and fast evaporation. The addition of some mineral spirits will slow down the evaporation (Modestini, Personal communication 1995). One conservator reports having seen it thickened by letting it evaporate in an open container prior to use (Zuccari, Personal communication 1995). Dianne Dwyer Modestini mentions mixing in some Picture Varnish Glossy to increase the desired gloss and viscosity (Dwyer 1992, 121).

(c) Picture Varnish-Mat

No information on the use of this as a brush coating by conservators.

(2) TYPICAL SPRAY SOLUTIONS

(a) Picture Varnish-Glossy

Used with the addition of turpentine or mineral spirits to achieve desired handling properties.

(b) Retouching Varnish

Often used undiluted but can be diluted with turpentine or a small amount of mineral spirits.

(3) ADDITIVES

(a) Picture Varnish Glossy

Turpentine and mineral spirits are commonly added to dilute it; wax or fumed silica can be added as matting agents to a brush coat (Dwyer 1992, 121).

(b) Retouching Varnish

Turpentine or a small amount of mineral spirits can be added to the varnish to slow down its evaporation rate or dilute it; wax or fumed silica can be used as matting agents (Dwyer 1992, 121). In the 1960s, Marco Grassi used BASF's Plastomol® as a plasticizer to reduce brittleness, recommended by Paolo Mora (Rome). But it is no longer commercially available (Grassi, Personal communication 1995).

(c) Picture Varnish-Mat

Although in the CCI Varnish Conference handbook Scott Williams states that no matting agent was detected in the analysis of Talens Rembrandt® Picture Varnish-Mat (Carlyle and Bourdeau 1994, Appendix IV, Scott Williams, Notes on Table 1), the manufacturer states that there are wax-based matting agents and analyses by S. Lomax of the National Gallery of Art Scientific Research Department confirmed the presence of wax (see (3)(a) above) (Lomax 1997).

(d) HALS

De la Rie reports that Laropal® K80 is not effectively stabilized by HALS (de la Rie 1990, 160–4; de la Rie 1993, 568).

Working Characteristics and Practical Properties

(1) APPEARANCE

It is one of the “best looking” varnishes available and has a rich gloss which is “softer” than the natural resins and with excellent saturation. It is wonderful to work with (from conversations with conservators who use it).

(2) BRUSHING

(a) Open/Working Time

Much shorter for the Retouching Varnish than for the Picture Varnish-Glossy due to the faster evaporation of its solvent mixture. Otherwise, similar to varnishes with White Spirit or turpentine solvent bases. The addition of mineral spirits can slow down the working time.

(b) Drying time

As under “Working time” above, faster for the Retouching Varnish, depends on solvent.

(c) Usual application

Both varnishes are applied as isolating layers and final surface coatings. The brush application technique can involve “lots of brush work”, “scrubbing it in” well with the brush (Prins, Personal communication 1995). A more matte final appearance can be achieved by vigorous brushing rather than by adding wax or any matting agent. A common use of the Talens Picture Varnishes is described below under Modifications for Special Applications/Tricks of the Trade in which it is interlayered with a thin spray application of poly(vinyl acetate). The poly(vinyl acetate) provides an isolating layer over poly(vinyl acetate) inpainting on the Talens initial brush coat to allow for brushing of a final Talens coat without picking up the previous coats and inpainting (Dwyer 1992, 121–2).

(3) SPRAYING

(a) Open/Working time

Because of the fast-evaporating solvents it contains, the Retouching Varnish can produce a very dry spray. This can be manipulated by the usual methods, solvent additives, distance from the painting, spray gun apertures.

(b) Drying time

Depends on solvents and factors mentioned above.

(c) Usual application

Can be sprayed as usual with appropriate manipulation of spray gun and the percentage of solvent added to the varnish mixture. It is very common for the final surface coating layer not be sprayed, to avoid a sprayed texture. However, a sprayed coat of the Retouching Varnish can be used to matte down an overly glossy brushed layer (Dwyer 1992, 121).

(4) MODIFICATIONS FOR SPECIAL APPLICATIONS AND EFFECTS/TRICKS OF THE TRADE

(a) Use of a poly(vinyl acetate) isolating layer

In the 1992 AIC Paintings Specialty Group Postprints, Dianne Dwyer describes a varnishing technique used by Mario Modestini that interlayers brushed Talens varnish layers with a thin, sprayed poly(vinyl acetate) layer and “gives an evenly sealed, evenly absorbing surface and allows the conservator to apply a second or third brush varnish without picking up the previous varnish.” The article itself should be read for the practical detail it contains, including the following: after the first coating of Talens varnish is applied and the retouching in PVA Mowilith® 20 (replacement for PVA AYAB) is complete, any matte areas can be brought up to surface gloss by locally varnishing with either one of the Talens varnishes, or the PVA Mowilith® 20; the surface is then sprayed with PVA Mowilith® 20 in alcohol and acetone as a light spray, a few times, manipulating the spray gun and distance as, appropriate, to avoid resin dust; after 24 hours the Talens varnish can again be brush-applied. The process can be repeated as necessary but usually only two Talens varnish coats do the job (Dwyer 1992, 121–2).

(b) Combined Sprayed and Brushed Application of Talens Varnish for the Final Coating

Marco Grassi's technique for getting an evenly distributed, light final brush coating over the poly(vinyl acetate) interlayer involves holding a small varnish spray gun in one hand and a brush in the other. The varnish is lightly sprayed onto the painting's surface at an angle while brushing the paint surface with the brush. This allows for a better distribution of the varnish without getting too much material in one area, which could happen with the straight brush application, and could affect the inpainting under the thin poly(vinyl acetate) layer. To do this, a light varnish mixture is made by feel, or a thicker one for more saturation, the painting is placed horizontally with overhead lights to allow a good view of the surface under the glare. The spray gun is aimed diagonally. This technique allows a shorter exposure of the recently applied lower varnish layer and inpainting to the solvents in the varnish coating being newly applied.

(c) To Matte Down an Overly Glossy Final Brush Varnish

Spray a fast-evaporating solvent (trichlorethane, or preferably a less toxic equivalent) with a small amount of white bleached beeswax (a disk about the size of a dime per six ounces of solvent). After a few hours, polish the surface or brush fairly vigorously with a soft but firm dry brush (Dwyer 1992, 121).

Aging Characteristics

Scientific information on the aging process of the Talens picture varnishes is not available. The reader is referred to the entry on Laropal® K80, the base resin for the Talens varnishes, and reminded of the known additives, castor oil in the Picture Varnish-Glossy, waxes in the Picture Varnish-Mat. Laropal® K80 yellows much less than the natural resins, but shares the brittleness and tendency to lose solubility on aging common to ketones (see Laropal® and MS2A® entries). However, Dianne Dwyer states, “In a survey of paintings in eighteen Kress regional galleries completed a few years ago, paintings varnished using this technique (PVA AYAB between Talens Rembrandt Varnish layers) had held up exceptionally well. After nearly thirty years, the surfaces had retained a pleasant sheen and the varnish had not noticeably discolored. … By comparison, paintings varnished a few years earlier by the same conservators using damar varnish showed significantly more yellowing” (Dwyer 1992, 121–2).

Health and Safety

The material safety information is similar for both the Picture Varnish-Glossy and the Picture Varnish-Mat (Materials Safety Data Sheet).

Dangerous Components:	White Spirit	Turpentine Oil
(Glossy)% by Weight:	20 – 35%	30 – 45%
(Mat) % by Weight:	0	over 70%

Flash Point: Glossy – ca. 37°C; Mat – ca. 34°C

Hazards Identification: Flammable. Health effects in case of excessive inhalation and ingestion. Eye and skin contact may cause irritation.

Emergency and First Aid Procedures:

eyes: Flush immediately with large amounts of water for 15 minutes. Consult a physician.

skin: Wash affected areas with soap and water. Remove contaminated clothing.

ingestion: Drink one or two glasses of water to dilute. Do not induce vomiting. Consult a physician.

inhalation: Move to fresh air.

Precautions to be taken in handling and storage: Use only in well ventilated areas. Store containers out of sun and away from heat, sparks, and flame. In case of accidental release, provide sufficient ventilation, remove all sources of ignition, absorb on a suitable substrate.

Exposure Controls: Provide sufficient ventilation to keep vapor concentration low. Use protective gloves in case of prolonged or repeated contact. Wash hands before eating, drinking, or smoking.

Disposal (MSDS)

Comply with local regulations.

Recently Introduced Low Molecular Weight Resin Varnishes

Regalrez® 1094

[100% hydrogenated oligomers of styrene and alpha-methyl styrene]

Historical Background

(1) INDUSTRIAL USE/ARTISTIC USE

Primarily used in formulations of hot-melt adhesives as a tackifier. Also recommended by the manufacturer for use in plastic modifications, adhesives, coatings, sealants, and caulks (Hercules, Technical Information Sheet 1994). Recently introduced as the primary component of Gamvar®, a proprietary picture varnish (Gamblin Artists' Colors Co., Portland, Oregon) For use on oil, acrylic, and alkyd paintings.

(2) CONSERVATION USE

Potential use in conservation as picture varnish suggested in 1990 (de la Rie and McGlinchey 1990b). Has been used as a conservation picture varnish since 1991.

Source

(1) PHYSICAL FORM

Solid, colorless, mixed translucent flakes and white powder.

(2) ORIGIN AND MANUFACTURE

Made from pure monomer hydrocarbon feed stocks including, but not limited to, styrene and alpha-methyl styrene (Hercules, personal communication) by: Hercules Inc. Hercules Plaza Wilmington, DE 19894–0001 tel. (302) 594–5000.

(3) VENDORS

Regalrez® 1094, Regalrez® Kraton Tinuvin® Kit, and Gamvar® are available from Conservator's Emporium, Reno, NV; Regalrez® 1094 and Gamvar® from Conservation Support Systems, Santa Barbara, CA; Gamvar® from Gamblin Artists' Colors Co., Portland, OR, and Pearl Paint Co., New York and Washington, D.C. [See Appendix II: Directory of Vendors.]

Chemical and Physical Properties

(1) CHEMICAL CLASSIFICATION

100% hydrogenated, low molecular weight, hydrocarbon resin.

(2) CHEMICAL FORMULA/STRUCTURE

Chemical name: hydrogenated oligomer of styrene and alpha-methyl styrene.

(3) MOLECULAR WEIGHTS

Weight average molecular weight: 900 (de la Rie and McGlinchey 1990b, 168)

Number average molecular weight: 630 (de la Rie and McGlinchey 1990b, 168)

(4) VISCOSITIES OF STANDARD SOLUTIONS: NOT AVAILABLE

(5) SOLUBILITY

Shell Odorless Mineral Spirits/Shell Sol® 71	S
Stoddard Solvent/Shell Sol® 340 HT	S
Shell Mineral Spirits 145	S
Petroleum Benzine	S
Turpentine	S
Shell Cyclo Sol® 100/Shell Cyclo Sol® 53	S

Xylenes	S
Toluene	S
Isopropanol	I
Ethanol	I
Acetone	IC
Arcosolv® PM/1-Methoxy-2-propanol	I

Terms

S	Soluble	clear solution
SC	Soluble Cloudy	completely dissolved, slightly cloudy solution
SV	Soluble Viscous	clear, highly viscous solution
SR	Soluble Residue	residue on the bottom
PSG	Partially Soluble Gel	resin is dissolved in a clear soft gel in a two-phase mixture with solvent on top
PIG	Partially Soluble Immobile Gel	resin is dissolved in a hard gel in a two-phase mixture with solvent on top
IM	Insoluble Milky	insoluble but a minute fraction has swollen and whitened, solvent looks milky
IC	Insoluble Clear	insoluble but a small portion of the resin has swollen to the point that it is stuck to the bottom of the jar, solvent is clear
I	Insoluble	insoluble, undissolved resin sits in clear solvent

Examples: S to PSG = mostly soluble; PIG to I = mostly insoluble

See also Appendix I: Solubility Testing Description and Solvents Used in Testing.

(6) GLASS TRANSITION TEMPERATURE

33°C (Hercules, Technical Information Sheet), 43.8°C (de la Rie and McGlinchey 1990b, 168) (difference probably due to different experimental conditions).

(7) BRITTLENESS AND FLEXIBILITY

Brittleness and flexibility tests have not yet been conducted. Mar resistance tests (de la Rie 1993) show Regalrez® 1094 to be comparable to damar and poly(vinyl acetate) (AYAA) and more resistant to scratching than mastic, ketone resins, and Arkon® P–90. Comparing the glass transition temperature (Tg) can provide insight into the brittleness of a material, although molecular weight may be a better indicator. The low molecular weight of Regalrez® 1094 suggests that it is a relatively brittle resin.

Preparation/Formulation

(1) TYPICAL BRUSH SOLUTIONS

Brush varnish concentrations can vary from 10–40 g/100 ml of solvent depending on the substrate and the effect you are trying to achieve. If used alone, 20–25 g/100 ml is usually appropriate. Used over another varnish, 15–20 g/100 ml can be used. Regalrez® must be sprayed when being reapplied or the first layer will dissolve. If the surface to be varnished is uneven after varnish removal (areas of matte and gloss), begin with a higher concentration of 30–40 g/100 ml or a first coat of another resin (e.g., stabilized damar or B-72).

(2) TYPICAL SPRAY SOLUTIONS

Spray solutions vary but because this is a low molecular weight resin, very high concentrations can be used without clogging a spray gun. If Regalrez® is used as the only varnish layer, 20–25 g in 100 ml of solvent gives a saturated surface. For application over an existing varnish, 15–20 g in 100 ml of solvent is usually sufficient.

(3) ADDITIVES

(a) Tinuvin® 292, a hindered amine light stabilizer (HALS), is recommended at 2% to the weight of the resin. The solvent is then added to the desired amount and will not affect the Tinuvin® 292 concentration (de la Rie and McGlinchey 1990b, 172). See also Section VII.A., Phenolic Antioxidants, Stabilizers, and UV Absorbers.

(b) Kraton® G series rubbers made by Shell Chemical were tested to see if the addition of a polymer would reduce brittleness and improve brushability (de la Rie 1993). These polymeric synthetic rubbers were added in small amounts to see if they could help mimic the unique handling properties of natural resins (which have a naturally occurring polymeric fraction). The rubbers are copolymers of styrene and ethylene butylene (the final structure is styrene-ethylenebutylene-styrene) (Kraton Polymers for Coatings). The rubbers were selected because they are relatively stable (when combined with Tinuvin® 292) and are soluble in low aromatic hydrocarbons. Two rubbers were selected: Kraton® G 1650 is in the form of a white powder and is of a higher molecular weight than the Kraton® G 1657 which comes in translucent pellets (Kraton Polymers for Coatings). Both of these Kraton® rubbers will dissolve slowly in Shell Solvent® 340 HT (0.4% aromatic). These Kraton® rubbers will dissolve more quickly with the addition of a few percent of an aromatic solvent. The glass transition temperature of the rubbers has not been measured because of the complexity of measuring the Tg of copolymeric structures but tests indicate that the addition of the rubber will make a more flexible final film. The addition of Kraton® G rubber to a Regalrez® varnish will improve scratch resistance of the film (de la Rie 1993). In age tests at the National Gallery of Art, the synthetic rubbers Kraton® G 1657 and Kraton® G 1650 remained unchanged in concentrations of up to 10% to the weight of the resin (Regalrez®) when Tinuvin® 292 was added at 2% to the weight of the combined resins (de la Rie 1993). The aesthetic effects have not been absolutely determined. In practice, with concentrations of rubber higher than 3%, the varnish will begin to have an appearance similar to a synthetic polymer. The addition of 1–3% rubber to the weight of the resin increases viscosity and gives a feeling of resistance when the varnish is brush applied (closer to the feel of a natural resin). In some instances, the addition of Kraton® G rubber to a Regalrez® varnish will prevent the low molecular weight resin from “sinking in.” Kraton G® is not an essential ingredient. A “good” solvent (one that quickly dissolves the rubber) like xylene, will make a less viscous solution than a “poor” solvent such as Shell Sol® 340HT (personal experience).

(4) SPECIAL CONSIDERATIONS

The solvent selected may affect the appearance of the final film. The effects of solvents on the final appearance and morphology of the varnish layer will be studied at the National Gallery of Art in the coming year (1997–98). A favorable aspect of this resin is that it can be dissolved in aliphatic hydrocarbon solvents (no aromatic content). Shell Solvent® 340 HT (0.1% aromatic) has an evaporation rate (1725 seconds to 90% evaporation) that permits adequate brushing time while becoming tacky soon enough that the gloss can be modified with dry brushing. A badger blender works well for dry brushing. Another useful property of Regalrez® is that it is insoluble in polar solvents like acetone, ethanol, or isopropanol. Inpainting systems that employ the use of alcohol (PVA, Paraloid® B–72) work extremely well on top of this resin.

(5) STORAGE/SHELF LIFE

Two years in dry powder form (as determined by the manufacturer for industrial use), several months in solution, four weeks if stabilized with Tinuvin® 292 (de la Rie and McGlinchey 1990b).

(6) OTHER

Regalrez® 1094 and the rubber can be dissolved right in a jar without filtering through a stocking or cheesecloth. Tiny cardboard bits have been noticed in the Kraton® samples so these should be removed before adding to the varnish (or filtered after mixing).

Working Characteristics and Practical Properties

(1) APPEARANCE

Saturates and exhibits gloss similar to a ketone or natural resin. It is slightly more glossy than ketones and natural resins and less glossy than Arkon® P-90 (de la Rie 1993).

(2) BRUSHING

Open/Working Time: From 30 seconds to 10 minutes depending on solvent selection and circumstances. When Arkon® P-90 and Regalrez® 1094 were first introduced, they were mixed in solvents like Shell Sol® 71 (72) (Leonard 1990) that has an evaporation time of 5140 seconds to 90% evaporation (n-BuOAc .09) (Shell hydrocarbon chart SC: 1056–94). There is anecdotal and scientific evidence that these resins have an affinity for the hydrocarbon solvents they are mixed in, which makes them dry more slowly. If this is so, then using such a slow evaporating solvent will give very long working times which may be useful when brush varnishing large paintings. For this reason, a somewhat faster evaporating solvent like Shell Solvent® 340 HT (0.4% aromatic and 1725 seconds to 90% evaporation) works well for more general applications. Solvents or solvent blends in this evaporation range give sufficient brushing time and yet will evaporate fast enough that the varnish will begin to dry as you work and give a feeling of resistance to the brush. It is at this point that the varnish can be quickly brushed out (buffed) with a dry badger hair blending brush. It is not yet known if this technique merely picks up varnish or results in a manipulation of the surface of the varnish (and if the manipulation will be permanent or if the resin will continue to level out). SEM studies at the National Gallery of Art in the coming year (1998) will compare application techniques and solvent selection with different resins to determine which factors affect surface morphology. Recent attempts at brush applying Regalrez® in petroleum benzine in a spray booth were not completely successful because the air being pulled across the surface caused the varnish to dry too quickly and resulted in an uneven surface.

Drying Time: The drying time is somewhat dependent upon solvent selection. Some conservators have remarked that Regalrez® is slow drying. It is dry to the touch in a few minutes when applied as above. Addition of Kraton® G rubber and the use of a slow evaporating solvent will increase drying time.

(3) SPRAYING

Open/Working Time: The best results have been achieved using a high volume low pressure sprayer like Chiron®, or an airbrush standing 2–4 feet from the picture. The varnish will feel dry to the touch almost immediately if it is sprayed in a spray booth and mixed in a fast evaporating solvent like petroleum benzine (evaporation rate same as toluene). If mineral spirits or Shell Sol® 340 HT is used, you will have time to brush out the varnish before it dries.

(4) MODIFICATIONS FOR SPECIAL APPLICATIONS AND EFFECTS/TRICKS OF THE TRADE

(a) After brush applications, quickly brush the surface with a dry badger hair blending brush to pick up excess varnish and give a more satiny surface (a practice commonly used with mastic and damar).

(b) To matte down an initial brush varnish of Regalrez®, apply 15–20 g in 100 ml of petroleum benzine, a fast evaporating naphtha, or Shell Cypar® 9. Regalrez® spray applied in petroleum benzine has also been used to give a cleaned painting the appearance of healthy, unvarnished oil paint. The spray application technique greatly affects the final gloss. A dry spray application yields a more matte surface.

The varnish can also be made somewhat matte by adding wax (one big “pea” of wax per 100 ml of solvent) using a low resin concentration and a fast evaporating solvent. You must add very high concentrations of wax or fumed silica to achieve a matte varnish with this resin. Regalrez® 1094 may not be the best resin to use as a starting point for a matte varnish because of the inherent gloss.

(c) Although Regalrez® was introduced to conservation as a substitute for natural resins, it can be used to even gloss on modern paintings, too. It has been applied both locally and overall to even out areas of matte and gloss that may have aged differently or appeared uneven after varnish removal. Regalrez® has been successfully used on modern pictures and naive or folk art paintings to resaturate the paint while preserving brush strokes, paint character, and matte/gloss differences without giving the appearance of an overall varnish. When the choice is made to apply varnish to originally unvarnished surfaces, Regalrez® 1094 may be a good choice because it can be applied and removed with aliphatic hydrocarbons.

(d) On panel paintings or pictures with smooth surfaces, you can apply the varnish with a cotton ball wrapped in silk. Tamp the ball on a blotter and rub in small circles for less gloss and good saturation (Proctor 1994, personal communication).

(5) OTHER

The ready solubility of the resin can be a drawback in some instances. It is not possible to reapply a brush varnish of Regalrez® over Regalrez® or to reapply any other varnish that is dissolved in hydrocarbon solvents. Attempts to locally resaturate or “go back into” small areas can cause pooling of the underlying Regalrez®. On the other hand, spray applications can be successfully applied over a spray or brush layer of Regalrez®. It is recommended that you use a more dilute solution for the spray (10–20 g of resin per 100 ml of solvent), a fairly fast-evaporating solvent (with an evaporation rate of 1,800 seconds to 90% evaporation or less) and stand two to four feet away. The best results have been achieved with Chiron and other high-volume, low-pressure sprayers and with airbrush applications. If you stand too close or use a wet spray, the first application may reticulate. These varnishes can be very glossy if applied in too high a concentration, in a very slow-evaporating solvent, or if not sufficiently brushed out. The high gloss of Regalrez® will die down only slightly after drying.

Aging Characteristics

(1) CHEMICAL PROCESS

Primarily photochemically (ultraviolet/visible radiation) initiated autoxidation (de la Rie and McGlinchey 1990b, 170).

(2) RESULTANT CHEMICAL AND/OR PHYSICAL ALTERATIONS

Accelerated aging tests were performed at the National Gallery of Art using a xenon arc weatherometer with both unstabilized and stabilized films of Regalrez® 1094. After 4,679 hours of aging, the infrared spectra (showing the formation of carbonyl, hydroxyl, and carboxylic acid groups as a result of aging) of Regalrez® 1094 stabilized with 0.5% Tinuvin® 292 remained unchanged. After 1,700 hours of aging, unstabilized films were so embrittled that testing had to be discontinued (de la Rie 1993). Films stabilized with 0.5–2% Tinuvin® 292 were still adhered to the glass testing support after 6,000 hours of aging. Tests for insoluble material were undertaken and no insolubility caused by crosslinking occurred in unstabilized Regalrez® after 1,900 hours of aging and in films stabilized with 0.5% Tinuvin® 292 after 2,269 hours of aging (de la Rie 1993).

(3) IMPACT ON VISUAL APPEARANCE, SOLUBILITY, AND REMOVABILITY

Regalrez® 1094 has not yellowed in any aging tests at the National Gallery of Art (unpublished data, National Gallery of Art). Unstabilized films of Regalrez® 1094 remained soluble in 100% cyclohexane after 1,700 hours of aging (but were extremely embrittled) (de la Rie 1993). Films stabilized with 0.5–1% Tinuvin® 292 remained soluble in 100% cyclohexane after over 6,000 hours of aging (unpublished data, National Gallery of Art).

When Regalrez® 1094 was combined with Kraton® G 1652 and 2% Tinuvin® 292, no solubility changes were noted after 2,269 hours of aging. The carbonyl index (degradation products) remained virtually unchanged in these same films after over 5,000 hours (de la Rie 1993).

(4) ATTRACTION AND RETENTION OF DIRT AND GRIME

Untested, but unlikely to attract dirt because of the high glass transition temperature.

(5) THEORETICAL LIFETIME

The solubility and carbonyl value as indicated by infrared spectrographs all remained constant after over 2,000 hours exposure in a xenon arc weatherometer (de la Rie 1993). Stabilized Regalrez® is predicted to be one of the most stable products used in conservation today.

Health and Safety

(1) HMIS RATINGS

Health hazard	0	Minimal
Flammability hazard	1	Slight
Reactivity hazard	0	Minimal

(2) EMERGENCY OVERVIEW

Static charges by emptying package near flammable vapors (i.e., solvent vapors) may cause flash fire; may form flammable dust/air mixtures.

(3) POTENTIAL HEALTH EFFECTS

May cause eye irritation by abrasion. Inhalation of dust may cause respiratory tract irritation. Wash thoroughly after handling and before eating, drinking, or smoking.

Disposal

The recommended disposal method is incineration in accordance with applicable regulations. Land filling in a permitted solid or hazardous waste facility, meeting technical regulatory requirements, is considered a suitable alternative.

Arkon® P-90

[a fully saturated alicyclic hydrocarbon, the C9 hydrogenated hydrocarbon resin]

Historical Background

(1) INDUSTRIAL USE

Arkon® resins were developed for use as tackifiers for pressure-sensitive adhesives (Arakawa Technical Data: ARK-001). They are also used industrially as gloss modifiers in paints and tackifiers in adhesives (de la Rie and McGlinchley 1990, 169).

(2) CONSERVATION USE

The introduction of Arkon® P-90 and its adaptation to the field of painting conservation is a result of research conducted by E René de la Rie and Christopher W. McGlinchey (de la Rie and McGlinchey 1990, 563–7; de la Rie and McGlinchey 1993, 566–73).

Source

(1) PHYSICAL FORM

Dome-shaped, colorless, translucent pellets.

(2) ORIGIN AND MANUFACTURE

“Hydrogenation for increased stabilization was recognized as early as 1940 when the hydro-genation of coumarone indene resins yielded materials that were ‘extremely resistant to ultra-violet light and atmospheric oxidation…’” (Fleck 1945, 298–9, cited in McGlinchey 1990, 565).

“Hydrogenated hydrocarbon materials currently available are converted from cracked C9 or C10 petroleum fractions and converted into oligomers. Arkon® (Arakawa Chemical) and Regalrez® (Hercules) products are based on isomers of C9 unsaturated carbons. In each case, once the feed stock is polymerized it is then hydrogenated under high pressure and temperature to remove nearly all of the unsaturation…” [These materials] are either cyclic, or highly branched species that when polymerized terminate to a low molecular weight; hence the final product is oligomeric” (McGlinchey 1990, 564–5).

(3) MANUFACTURERS AND VENDORS

Arkon® P-90 is manufactured in Japan. This product is available through Arakawa Chemical in Chicago. Hercules Co. also produces almost the same product in the Netherlands. Arakawa Chemical Inc. North American distributors are as follows: Quadra Chemicals Ltd. (Canada), Burlington, Ontario; Chem-Materials Co., Cleveland, Ohio; The Chidley & Peto Co., Arlington Heights, Illinois; and Focus Chemical Co., Portsmouth, New Hampshire. Arkon® P-90 is also available from Conservator's Emporium, Reno, NV. (See Appendix II: Directory of Vendors.)

Chemical and Physical Properties

(1) CHEMICAL CLASSIFICATION

Arkon® P-90 is a fully saturated alicyclic hydrocarbon (Arakawa Chemical product literature and D. Nagasawa, Manager, Sales and Marketing, Arakawa Chemical (U.S.A.), Inc., personal communication). “Some products are derived from the dicyclopentadiene, a C10-molecule, while others are obtained by oligomerization of C9 isomers or pure alpha-methylstyrene. These resins contain residual unsaturation that can be removed by hydrogenation” (de la Rie and McGlinchey 1990, 160).

(2) CHEMICAL FORMULA/STRUCTURE

(de la Rie and McGlinchey 1990, 170)

(3) MOLECULAR WEIGHTS

Weight Average Molecular Weight: 934 (de la Rie and McGlinchey 1990, 168) Number Average Molecular Weight: 620 (de la Rie and McGlinchey 1990, 168).

(4) REFRACTIVE INDEX

1.522 (at 20°C) (de la Rie and McGlinchey 1990, 168).

(5) SOLUBILITY

100% hydrogenated, low molecular weight, hydrocarbon resin.

Shell Odorless Mineral Spirits/Shell Sol® 71	S
Stoddard Solvent/Shell Sol® 340 HT	S
Shell Mineral Spirits 145	S
Petroleum Benzine	S
Turpentine	S
Shell Cyclo Sol® 100/Shell Cyclo Sol® 53	S

Xylenes	S
Toluene	S
Isopropanol	I
Ethanol	I
Acetone	IC
Arcosolv® PM/1-Methoxy-2-propanol	I

Note: “Non[-]polar resins lack carbonyl and hydroxy groups. This accounts for their insolubility in such polar solvents as acetone and ethanol” (McGlinchey 1990, 565).

Terms

S	Soluble	clear solution
SC	Soluble Cloudy	completely dissolved, slightly cloudy solution
SV	Soluble Viscous	clear, highly viscous solution
SR	Soluble Residue	residue on the bottom
PSG	Partially Soluble Gel	resin is dissolved in a clear soft gel in a two-phase mixture with solvent on top
PIG	Partially Soluble Immobile Gel	resin is dissolved in a hard gel in a two-phase mixture with solvent on top
IM	Insoluble Milky	insoluble but a minute fraction has swollen and whitened, solvent looks milky
IC	Insoluble Clear	insoluble but a small portion of the resin has swollen to the point that it is stuck to the bottom of the jar, solvent is clear
I	Insoluble	insoluble, undissolved resin sits in clear solvent

Examples: S to PSG = mostly soluble; PIG to I = mostly insoluble

See also Appendix I, Solubility Testing Description and Solvents Used in Testing.

Preparation/Formulation

(1) TYPICAL BRUSH SOLUTIONS 25% (Leonard 1990, 175)

(2) TYPICAL SPRAY SOLUTIONS 25% (Leonard 1990, 175)

(3) ADDITIVES

(a) Tinuvin® 292 hindered amine light stabilizer (Ciba-Geigy) has been shown to slow the effects of aging on films of Arkon® P-90 (de la Rie and McGlinchey 1990, 170–2).

(b) Polymer additives (Kraton® G1650 & G1657, Hercules) may reduce brittleness and lower the gloss (de la Rie 1993, 566–73).

(4) STORAGE/SHELF LIFE

Discussion of the shelf life took place at the IIC 1994 Ottawa conference, Varnishes, Authenticity and Permanence, during which de la Rie stated that these resins should not be predissolved in solvent for more than a few weeks. Moreover, if hindered amine light stabilizers (such as Tinuvin® 292) are used with Arkon® P-90, the same recommendation which he gives for its use with damar should apply, that is, the solutions “… should be prepared shortly before application. Shelf life of such solutions is relatively short” (de la Rie 1989, 144).

Working Characteristics and Practical Properties

(1) APPEARANCE

Arkon® P-90 has excellent saturating capability. It can be very glossy.

(2) BRUSHING

(a) Open/Working Time

Due to its ease of solubility in aliphatic hydrocarbon solvents having a wide range of evaporation rates, Arkon® P-90 has variable working time depending on the diluent. Solvents with slow evaporation rates allow for final “brushing out” with a natural bristle brush, such as badger hair, thereby allowing for a thin coat which also helps to control the gloss level (Personal experience; experiments done at the J. Paul Getty Museum, 1989–90; see also Leonard 1990).

(b) Drying Time

It is dependent on the evaporation rate of the diluent used. 25% solutions in Shell Sol® 71 tested on a 17th-century Dutch portrait remained tacky for several days (Experiments done at the J. Paul Getty Museum, 1989–90; Leonard 1990).

(3) SPRAYING

Successive passes with the spray gun can cause running and/or reticulation, depending on the evaporation rate of the diluent (Personal experience). Open, working, and drying times are similar to brush applications and are all dependent on diluent (Personal experience; experiments done at the J. Paul Getty Museum, 1989–90; Leonard 1990).

(4) MODIFICATIONS FOR SPECIAL APPLICATIONS AND EFFECTS/TRICKS OF THE TRADE

(a) Color Saturation

Arkon® P-90 is very effective in saturating colors on traditional oil paintings. Tests conducted at the J. Paul Getty Museum in 1989–90 on a Dutch portrait demonstrated that the resin was virtually indistinguishable from a mastic resin (Leonard 1990, 175).

(b) The silica matting agent from Soluvar® Matte Varnish has been used by successive rinsing of the Soluvar® with xylene, decanting off the solvent to obtain the settled matting agent and then adding it at a 5–10% (to weight of the resin) to Arkon® P-90 (Chris Stavroudis, painting conservator and personal experience).

(c) Effect on Desired Surface Gloss

The 50% solution has been determined by practitioners to be far too glossy (Experiments at the Getty Museum, 1990). A very thin layer of the 25% solution was acceptable but the gloss level in Shell Sol® 71(72) was found to be difficult to control in tests at the Getty Museum.

A spray application of B-72 over Arkon® P-90 was reported as being successful in reducing the gloss (conversation with Victoria Montana Ryan, paintings conservator).

(d) Isolating and/or providing a foundation for subsequent surface applications Inpainting over an Arkon® P-90 isolating varnish has been done successfully with pigments ground in the resin (conversation with Hays Shoop, painting conservator).

(e) Due to the ease of solubility, Arkon® P-90 might be considered for a temporary, “working” varnish.

(5) OTHER

(a) Because Arkon® P-90 is so readily soluble in hydrocarbon solvents, inpainting with a medium dissolved in xylene can have a deleterious effect on the surface quality; the resin/inpaint medium can cause minute dots rather than the desired evenness (Personal experience).

(b) Characteristics

colorless and odorless

excellent tack, adhesion, and cohesion

excellent weather resistance

excellent heat resistance

widely ranged compatibility and solubility with elastomers and solvents stable supply

(ARK-001, Arakawa Technical Data)

(c) Special Considerations

The gloss level of Arkon® P-90 is sometimes difficult to control and problems of evenness, when a glossy surface was desired, have been reported (conversation with Chris Stavroudis, paintings conservator and experiments done at the J. Paul Getty Museum, 1989–90; Leonard, 1990).

Aging Characteristics

(1) CHEMICAL AGING

“Upon aging the polarity of the [synthetic low molecular weight] resins increases as a result of formation of species containing ketone, hydroxyl and carboxylic acid groups, and the films require more polar solvents for removal” (de la Rie 1993, 567–8).

Arakawa Chemical reports in its product literature, regarding Arkon® P-90's resistance to heat that after six hours at 250°C, very little color change was noted.

(2) RESULTANT CHEMICAL AND/OR PHYSICAL ALTERATIONS

(a) Impact of Aging on Solubility

“The two HHC [hydrogenated hydrocarbon] resins … remain removable in a solvent mixture that is not “stronger” than 50/50 toluene/cyclohexane. However, both [Arkon® P-90 and Regalrez® 1094 (Hercules)] HHC resins were severely embrittled after 1700–1900 hours” (de la Rie 1993, 568). In addition, “Both HHC resins … are stabilized significantly by Tinuvin 292 (hindered amine light stabilizer)” (de la Rie 1993, 568). In the same study, the presence of insoluble material after aging was examined. De la Rie states that, “Although the unstabilized Arkon P-90 film is more than 90% insoluble in cyclohexane and toluene after 1900 hours of aging, it is almost completely soluble in acetone. This indicates that the resin is oxidizing but that no completely insoluble network is formed” (de la Rie 1993]], 569). Again, the effects of the addition of Tinuvin® 292 are demonstrated in the same study to have a significant effect. With the addition of 1% of additive, “… [the film] develops a small amount of material insoluble in cyclohexane in 1900 hours of aging, but is completely soluble in toluene and acetone.”

(b) Impact of Aging on Visual Appearance

Because Arkon® P-90 does not have a lengthy history of use among conservators, the impact of aging upon visual appearance could not be adequately addressed. (For comparison to mastic upon aging, see Leonard 1990.)

(c) Attraction and Retention of Dust and Grime

A disadvantage of the resin in a slowly evaporating solvent such as Shell Sol® 71, is that the surface remains tacky for a rather lengthy period and can absorb dust (Personal experience in experiments at the J. Paul Getty Museum, 1989–91).

(3) THEORETICAL LIFETIME

(a) “Varnish films have been tested in a xenon arc weatherometer in which daylight through window glass, including the ultraviolet component, is simulated. Under these conditions, varnishes formulated according to this instruction sheet proved stable for a minimum of 6000 hours” (Instruction Sheet supplied by the National Gallery, Washington, D.C., to participants of the conference, “Varnishes, Authenticity and Permanence,” Ottawa, 1994). In these instructions, “it is recommended that Tinuvin 292 always be incorporated at 2% the combined resin weight.”

(b) The most recent research on hydrogenated hydrocarbon resin varnishes suggests that Regalrez® 1094, the hydrogenated hydrocarbon resin produced by Hercules, Inc., is a more stable product (de la Rie 1993, 568). (See previous section on Regalrez® 1094.)

Health and Safety

The following data is from the Materials Safety Data Sheet for Arkon® P-90:

Flash Point (Method Used): 347'F (ASTM D-92–57)

Extinguishing Media: Carbon dioxide, dry chemical, or foam

Special Fire Fighting Procedures: Not known. However, firefighter should wear self-contained breathing apparatus to avoid inhalation of smoke and vapors.

Incompatibility: Strong oxidizing agents

Hazardous Decomposition or Byproducts: Thermal decomposition or combustion may produce carbon monoxide, carbon dioxide, ethane, etc.

Hazardous Polymerization: Not known

Health Hazard Data:

Primary irritation studies:

Inhalation: Not available

Skin: Mild irritation

Ingestion: Not known

Health Hazards (Acute and Chronic): Acute oral (mice) LD50 value is greater than 22.5 g/kg.

Carcinogenicity:

NTP: Not established

IARC Monographs: Not established

OSHA Regulated: Not established

Signs and Symptoms of Exposure: Not known

Medical Conditions Generally Aggravated by Exposure: Not known

Emergency and First Aid Procedures:

Eye/skin contact: Immediately flush with large amount of water. If irritation results, contact a physician.

Precautions to be Taken in Handling and Storage: Store in fairly dark, cool place and do not expose to direct sunlight for any length of time. To store under 100°F is recommended to prevent remassing.

Other Precautions: Avoid prolonged or repeated contact with resin dust or heated vapors. Wear proper protective equipment. Keep away from open flames.

Control Measures:

Respiratory protection should be worn to prevent inhalation of dust or heated vapors.

Ventilation

Local Exhaust: Suggested if heated or dust generated

Mechanical: Suggested if heated or dust generated

Special: Not necessary

Protective Gloves: Chemical-resistant plastic or rubber

Eye Protection: Chemical goggles recommended

Other Protective Clothing or Equipment: Not required

Waste Disposal Method

(1) Dispose of in chemical landfill or incinerate according to local, state, and federal regulations.

(2) Steps to be taken in case material is released or spilled: Sweep up with broom and shovel; place in a waste container; wear respirator if dust is generated.

Escorez® 5380

[a cyclo-aliphatic hydrocarbon resin]

Historical Background

(1) INDUSTRIAL USE

Escorez® 5380 is one of several Escorez® series polymers developed by Exxon Chemicals which are designed to tackify a variety of adhesive polymers, including EVA, APP, APAO, SIS, and SEBS block copolymers (Exxon Technical Data).

(2) CONSERVATION USE

Escorez® 5380 was tested for use as a varnish in the early 1990s by Gustav Berger, in response to research by de la Rie and McGlinchey. The mixture was sold and marketed by Conservator's Products Company as UVS Finishing Varnish. It sold in a 30 wt% solution dissolved in low aromatic hydrocarbons with the admixture of approximately 5 wt% of a proprietary plasticizer. It was first produced and marketed as a varnish in 1991. Escorez® 5380 ceased to be the base resin for Berger's UVS Varnishes in February 1996. (Personal communication between Dr. Chludzinski and Wendy Samet, 1997).

Source

(1) PHYSICAL FORM

A water white resin produced in small shards (Exxon Chemicals).

(2) ORIGIN AND MANUFACTURE

Its history and method of manufacture is similar to that already described for Arkon® P-90 (see previous section). It is formed from the polymerization of an impure petroleum fraction, then hydrogenated under high temperature and pressure to remove nearly all unsaturation.

(3) MANUFACTURERS AND VENDORS

Escorez® 5380 is manufactured by Exxon Chemical Company in the United States. It is available in its pure resin form from Exxon Chemical Company, Polymers Group-Americas, Atlanta, Georgia.

Chemical and Physical Properties

(1) CHEMICAL CLASSIFICATION

Escorez® 5380 is a cyclo-aliphatic hydrocarbon resin. It is in the form of a hydrogenated polystyrene.

(2) CHEMICAL FORMULA/STRUCTURE

The specific chemical formula was not found at the time of writing.

(3) MOLECULAR WEIGHT

Weight Average Molecular Weight: 518

Number Average Molecular Weight: 349

(4) REFRACTIVE INDEX: 1.548

(5) SOLUBILITY

No solubility testing (see Appendix I) was performed for Escorez®.

(6) GLASS TRANSITION TEMPERATURE: 31.5°C.

(7) BRITTLENESS AND FLEXIBILITY

No testing data is available. However, Escorez® 5380 has a relatively low glass transition temperature and flows together into large lumps when left on the shelf, indicating that it is probably relatively soft (nonbrittle).

Preparation/Formula

(1) TYPICAL BRUSH SOLUTIONS

30 wt% in low aromatic solvents (Berger, UVS Finishing Varnish manufactured by Conservator's Products Co.).

(2) ADDITIVES

Tinuvin® 292 hindered amine light stabilizer (Ciba-Geigy) has been shown to slow the effects of aging of Escorez® 5380 (de la Rie and McGlinchey 1990, 170–2).

(3) STORAGE/SHELF LIFE

The dry resin flows together into large lumps when left on the shelf for long periods of time. According to de la Rie, the dissolved resins should not sit on the shelf longer than three weeks.

Working Characteristics and Practical Properties

(1) APPEARANCE

Escorez® 5380 in a 30% dilution dries to a thick coating that is quite glossy. In a more dilute solution it dries to an even, well saturated, relatively pleasing gloss (author's own trials).

(2) BRUSHING

Open/Working Time: Due to Escorez® 5380's solubility in aliphatic hydrocarbon solvents, the conservator can choose from dozens of available hydrocarbon mixtures to obtain a desired working time. The author has found 15% Escorez® 5380 in Shell MS-135® to be a useful concentration for brushing (author's own trials).

(3) SPRAYING

The varnish can be sprayed successfully keeping in mind that the resin's relative solubility could make it susceptible to reticulation if care is not taken.

(4) OTHER

(a) Attraction and Retention of Dust and Grime

These characteristics are equal to those for Arkon® P-90 (see previous section).

(b) Characteristics

Colorless and odorless; wide-ranging compatibility and solubility with elastomers and solvents.

Aging Characteristics

In aging tests, de la Rie and McGlinchey show Escorez® 5380 to be quite stable, but on the whole somewhat less stable than the other hydrogenated hydrocarbon resins employed as varnishes (Arkon® P-90 and Regalrez® 1094). Tests show that Escorez® 5380 remains removable in a mixture of 50/50 cyclohexane/toluene, even after extensive aging. The results are markedly improved by the addition of a hindered amine light stabilizer (such as Tinuvin® 292) to the varnish (de la Rie and McGlinchey 1990).

Health and Safety

The following is from the Material Health and Data Sheet for the Escorez® 5000 Series

Flash Point: 410°F Method COC

Extinguishing Media: Water

Fire and Explosion Hazards: Airborne dust in high concentrations can explode

Decomposition products under fire conditions: No unusual ones

Health Hazard Studies

Eye Contact: Slightly irritating but does not injure eye tissue

Skin Contact: Frequent or prolonged contact may irritate

Inhalation: Negligible hazard at room temperature

Ingestion: Minimal toxicity

Emergency First Aid Procedures: For eye and skin contact, immediately flush with large amounts of water

Workplace Exposure Limits: Exxon recommends 10 mg/m³ total for nuisance dust

Personal Protection: Wear safety glasses with side shields, long sleeves, and chemically resistant gloves; wear respiratory protection where workplace limits may exceed airborne standards

Disposal

Dispose of according to state and location regulations.

Proprietary Varnishes Based on Recently Introduced Low Molecular Weight Resin Varnishes

UVS (Ultraviolet Stabilized) Finishing and Matte Varnishes

[hydrogenated hydrocarbon styrene and methyl styrene]

Historical Background

(1) INDUSTRIAL USE

See Section on Regalrez® 1094.

(2) CONSERVATION USE

Following publication of the research by de la Rie and McGlinchey (de la Rie and McGlinchey 1990), Gustav Berger and Dr. George Chludzinski, Chemist at Conservator's Products Company (CPC), used Escorez® 5380 to develop their first UVS varnish in the early 1990s. However, when the results of the CCI workshop on varnishes (Carlyle and Bourdeau 1994) became available, and showed that varnishes based on Regalrez® 1094 were less shiny and easier to apply than those made with Escorez® 5380, a switch was made to Regalrez® 1094. This switch to Regalrez® 1094 was made in February, 1996. At that time a UVS Finishing Varnish® and a UVS Matte Varnish® were formulated. There are no batch numbers or other indicators to distinguish between the two base resins, however very little of the Escorez® based varnish was sold, according to Dr. Chludzinski (Personal communication between Dr. Chludzinski and Wendy Samet, September 3, 1997). Practical uses of these varnishes were described by Gustav Berger in an article that appeared in two parts in The Picture Restorer (Berger 1995; 1996).

Source

(1) PHYSICAL FORM

These varnishes are sold by CPC in a 30% by weight solution in low-aromatic petroleum solvent with the admixture of less than 5% of a CPC proprietary plasticizer based on ethylene vinyl acetate (Telephone conversation between Dr. Chludzinski and Wendy Samet, September 3, 1997).

UVS Matte Varnish® is comprised of: Regalrez® 1094, Microsere 5906 (a microcrystalline wax), BASF Wax A (a synthetic wax), and 5% CPC proprietary solid plasticizer.

(2) MANUFACTURER AND VENDORS

UVS Matte and Glossy Varnishes are distributed by Conservator's Products Co., New York, and Talas, New York. (See also Appendix II, Directory of Vendors.)

Chemical and Physical Properties

(1) For varnish sold after February, 1996, see preceding section on Regalrez® 1094.

(2) For varnish sold before February, 1996, see preceding section on Escorez® 5380.

(3) SOLUBILITY

Shell Odorless Mineral Spirits/Shell Sol® 71	SC
Stoddard Solvent/Shell Sol® 340 HT	SC
Shell Mineral Spirits 145	SC
Petroleum Benzine	SC
Turpentine	S
Shell Cyclo Sol® 100/Shell Cyclo Sol® 53	S

Xylenes	S
Toluene	S
Isopropanol	I
Ethanol	I
Acetone	I
Arcosolv® PM/1-Methoxy-2-propanol	I

Terms

S	Soluble	clear solution
SC	Soluble Cloudy	completely dissolved, slightly cloudy solution
SV	Soluble Viscous	clear, highly viscous solution
SR	Soluble Residue	residue on the bottom
PSG	Partially Soluble Gel	resin is dissolved in a clear soft gel in a two-phase mixture with solvent on top
PIG	Partially Soluble Immobile Gel	resin is dissolved in a hard gel in a two-phase mixture with solvent on top
IM	Insoluble Milky	insoluble but a minute fraction has swollen and whitened, solvent looks milky
IC	Insoluble Clear	insoluble but a small portion of the resin has swollen to the point that it is stuck to the bottom of the jar, solvent is clear
I	Insoluble	insoluble, undissolved resin sits in clear solvent

Examples: S to PSG = mostly soluble; PIG to I = mostly insoluble

See also Appendix I, Solubility Testing Description and Solvents Used in Testing.

Preparation/Formulation

(1) TYPICAL BRUSH SOLUTIONS

(a) UVS Finishing or Matte Varnishes can be diluted by adding 5–15% VM&P naphtha (Manufacturer's recommendation).

(b) A small quantity of UVS Matte Varnish® added to the UVS Finishing Varnish® will soften the reflectance of the latter.

(c) The addition of small quantities, 2–3%, of Odorless Mineral Spirits will yield a slow-drying varnish for an even “brush out” over a large surface.

(2) TYPICAL SPRAY SOLUTIONS

The addition of 5–15% of a fast drying solvent, such as VM&P naphtha or heptane will yield a fast-drying mixture for spraying.

(3) ADDITIVES

Tinuvin® 292 (CIBA-Geigy) a HALS at 2% to the weight of the resin is packaged separately. The varnishes come mixed with a CPC proprietary plasticizer of less than 5%.

(4) STORAGE/SHELF LIFE

The shelf life is two years before the addition of the Tinuvin® 292. After the addition of the Tinuvin® 292, the shelf life is 3–4 weeks.

Working Characteristics and Practical Properties

(1) APPEARANCE

UVS Finishing Varnish® is a clear, colorless film with high gloss and saturation.

UVS Matte Varnish® has a silky finish which can be as matte as paper.

(2) MODIFICATIONS/TRICKS OF THE TRADE

(a) If leveling of the surface is required, UVS Finishing Varnish® can be rubbed by hand, when dry, just like mastic or damar varnish. UVS Matte Varnish® should not be rubbed.

(b) It is recommended to test varnishes on a piece of heavy Mylar, prior to use, to evaluate the appearance and working qualities. This is particularly important with matte varnishes.

(c) Because the varnish is not soluble in lower alcohols and acetone, it may be used to isolate successive coating or as an inpainting medium.

Aging Characteristics

See Regalrez® 1094 for aging characteristics of the resin.

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Wehlte, K. 1975. The Materials and techniques of painting. 2nd ed. New York: Van Nostrand Reinhold.

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Zora Pinney Archives in the Modern Materials Collection at National Gallery of Art with additional information from interviews by Paula Volent.

Zuccari, F. (Conservator). October 1995. Personal communication.

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¹A note about the spelling of “damar”: Throughout this volume the spelling with one “m” has been used, except in explicit quotations, per the first spelling found in Webster's Collegiate Dictionary, 10th edition, and Feller's “What's in a name: Dammar, or, serendipity in the library,” The Crucible 1964, 49:214, 216, 218.

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