Inpainting: Dyes

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Kremer Zapon Stains/Dyes

The Kremer Zapon stains have been used by some conservators as a way to intensify colors on an existing inpainting palette or as a glaze on top of areas if inpainting to adjust the color (see “Inpainting Application Techniques” below).

Format/Preparation of Use

The Zapon stains/dyes are metal-complex dyes manufactured in powder form and available through Kremer Pigments. The dry powder stains/dyes are available in the following colors:

94000 Nigrosin black x 51

94010 Yellow 157

94020 Red 471

94030 Blue 807

Preparation for Use

The dyes are soluble in various organic solvents including ethanol, isopropanol, 1-methoxy-2-propanol (commercially available as ArcosolvⓇ PM or SolvenonⓇ PM), and ethyl acetate. The yellow dye is also soluble in acetone. They are only partially soluble in hydrocarbon or aromatic solvents. The blue dye is soluble in toluene.

Typical preparation for use involves first making a solution of the dye in solvent, then adding that solution to an inpainting medium. Dispersion of the dye works best if the inpainting medium is already dissolved in its respective solvent. Some common examples include dry pigments mixed with MS2A or MS2B in Stoddard solvent or commercially available colors like Golden MSA paints mixed with xylenes. The Zapon dyes can be dissolved in a very small amount of alcohol, sometimes as little as a few drops, and then mixed into the medium by dispersing the dye with a brush. Using only a small amount of alcohol allows it to evaporate from the medium so that it won’t affect the working properties if hydrocarbon or aromatic solvents are being used. For inpainting palettes where the diluent has completely evaporated, it is possible to re-dissolve the colors with hydrocarbon or aromatic solvents even if they contain the Zapon dyes. After the initial mixing, the dye stays dispersed in the medium.

If the diluent for the inpainting medium has the same solubility range as the stains, then the stains can be added to the dissolved medium directly in powder form and then dispersed by brush. It is highly recommended that only a small amount of the powdered stain be added at a time due to its high tinting strength. The preferred way to control the intensity of the color is to follow the procedure described above and make a solution of the dye first, and then add it to the medium.

For ease of use, some conservators keep a small glass vial of each dye dissolved in ethanol and then add the dye solution to their palette as needed. An alternate method of preparation involves creating a separate palette with the dyes dispersed in an inpainting medium.¹ This makes it possible to have a clean dye palette that is available to be re-dissolved as needed to adjust the colors on a regular palette. The preparation of this palette is similar to the methods described above; the powdered dye is dissolved or wet up in a small amount of alcohol (typically ethanol), then the medium of choice is added on top of the dye solution. The dye should be completely mixed with or covered by the medium so that it does not powder and contaminate the other colors or increase the potential of inhalation or for getting the powder on clothes or skin.

The dyes can be re-dissolved in the same diluent used for the particular medium as long as the dyes are well dispersed when the palette is made. A separate dye palette makes the colors available to add as a glaze layer or to mix with other colors on a regular inpainting palette (see “Inpainting Application Techniques” below). Once the colors have hardened, the palette can be easily stored or transported.

Inpainting Application Techniques

Three inpainting approaches have been described for the Zapon dyes. The majority of conservators who have used the dyes mix them with dry pigments bound in PVAc. The most common solvent used for inpainting with the dyes is ethanol. In all descriptions, the dyes were added on top of one or more layers of isolating varnish, typically PVAc.

Intensifying Colors for an Existing Inpainting Palette

The dyes can be added to an inpainting palette to adjust colors made up of dry pigments bound in a medium or a commercially available paint (such as Golden PVA or Golden MSA). The method of adding the dye to colors already on a palette is dependent on the type of medium used (see preparation for use above). Adding the dye to a pre-mixed color makes it possible to shift the hue or temperature of that color or increase its transparency without losing a certain level of intensity. This approach has often been used for intensifying blacks, particularly in Northern European paintings. One benefit of using the dye to adjust a pre-existing color is that the color can be adjusted without building up thick layers with inpainting. In addition, some pigments can be coarse or relatively large in particle size, which can affect the texture of inpainting. Inpainting with the dyes does not alter the surface texture substantially, making the dyes a frequent choice for inpainting on smooth panel paintings or paintings on copper.

Applying an Intense Base Color

A relatively intense glaze of dye can be laid down on a fill as a base color, and then subsequent layers of inpainting can be applied on top to further adjust the color or texture.

Laurent Sozzani described his method for recreating certain glazing techniques as follows: “When I have a really hot glazed area, I have found that I have better luck doing the opposite of what the artist did…first I lay in the glaze, which is invariably too intense and too hot…over a base color, and then I scumble back over the glaze layer…and bring it to the correct tone” (personal communication, July 31, 2008).

Applying a Top Glazing Layer

The dyes have also been applied as thin, transparent glazes on top of a base color to adjust the tone or value of that underlying color. This glazing technique has also been used to simulate a “dirty varnish” appearance. The glaze can adjust old, discolored areas of inpainting or be applied to localized damages on a painting with a yellowed varnish if full treatment is not carried out. For this technique, conservators have often used a combination of the dyes, with the main portion of that mixture being the yellow dye. Combinations of black, red, and yellow have also been used to create a brown-colored glaze.

Color Characteristics

The Kremer Zapon dyes² have a high tinting strength and vary in intensity and coloring strength depending on the concentration of the dye in the medium and the thickness of the application. The value or lightness of the colors is also dependent on the concentration of the dye. The colors are very clean and provide relatively pure color.

The colors have been classified by a color index number, a standard classification system that is prefixed with the initials C.I. and followed by a number that identifies the color. The color index numbers are grouped in ranges according to chemical structure (See Table 1: Chemical Characterization below).

Qualitatively, the yellow dye is relatively warm in tone, which does not appear to change with varying concentration of the color. The red has been qualified as magenta in hue and is slightly cool in tone. Thinner glazes or washes of the red appear to be less cool than a more concentrated layer when observed on top of a white layer or ground. The blue has a slight greenish hue, similar to cerulean pigments. The blue has been combined with the yellow to achieve certain transparent shades of green. Some conservators prefer not to use the blue when trying to match colors such as azurite, smalt, ultramarine, or indigo in Old Master paintings.³ The black is relatively cool in tone; adding a small amount of yellow to the black produces a warmer hue.

Opacity/Transparency

The opacity/transparency of the dyes is dependent on the medium being used, the thickness of application, and the concentration of the dye in the medium. In higher concentrations, the dyes can provide a very intense color and appear almost opaque when applied over a fill. Lower concentrations of the Zapon dyes provide intense, transparent color. The transparent quality of the colors and the potential to achieve intense color in a thin layer have been the main reasons that conservators choose the Zapon dyes for inpainting.

Chemical Composition

Product literature from Kremer indicates that the stains/dyes are pure complex-metal dyes.⁴

Table 1: Chemical Characterization

Zapon Stain/Dye	Chemical Characterization
94000 Nigrosin black x 51	C.I. Solvent Black 27
94010 Yellow 157	C.I. Solvent Yellow 82
94020 Red 471	C.I. Solvent Red 118
94030 Blue 807	C.I. Solvent Blue 70, phthalocyanine metal complex

Chemical characterization provided on Kremer MSDS sheets. Last updated February 16, 2009.

Color Reactivity/Stability

Table 2: Chemical Reactivity/Stability

Zapon Stain/Dye	Chemical Reactivity/Stability	Hazardous Reactions
94000 Nigrosin black x 51	Negligible	Risk of dust explosion
94010 Yellow 157	Negligible	Risk of dust explosion
94020 Red 471	Negligible	Risk of dust explosion
94030 Blue 807	Humidity should be avoided, Thermal instability >220ºC	Risk of dust explosion

Details regarding chemical reactivity provided on Kremer MSDS sheets. Last updated February 16, 2009.

Lightfastness

The lightfastness⁵ of the dyes can differ depending on the binding medium, the concentration of the colorant, and the thickness of the layer (personal communication, Eva Eis, Kremer Pigmente, 2008).

Table 3: Lightfastness Ratings

Zapon Stain/Dye	Lightfastness
94000 Nigrosin black x 51	7-8
94010 Yellow 157	7-8
94020 Red 471	7-8
94030 Blue 807	7

The lightfastness ratings as provided by Kremer representatives are in accordance with ISO 105-A02 (assessment of change in shade) and ISO 105-A03 (assessment of bleeding) (personal communication, Birgit Schiemann, Kremer Pigmente, 2008).

Toxicity

Table 4: Health Hazards

Zapon Stain/Dye	Health Hazards
94000 Nigrosin black x 51	Hazard designation unknown Contact with skin/eyes/clothing, inhalation, and ingestion should be avoided.
94010 Yellow 157	Environmentally hazardous: very toxic to aquatic organisms Contains 6% complex-bound chrome. Contact with skin/eyes/clothing, inhalation, and ingestion should be avoided.
94020 Red 471	Contains cobalt. Contact with skin/eyes/clothing, inhalation, and ingestion should be avoided.
94030 Blue 807	Not considered hazardous according to EEC Directives 67/548/EEC and 88/379/EEC Contact with skin/eyes/clothing, inhalation, and ingestion should be avoided.

Toxicity information provided on Kremer MSDS sheets. Last updated February 16, 2009.

Table 5: Recommended Safety Protection

Recommended Personal Protection
Protective gloves	EN 374 Nitrile rubber (0.4mm) Chloroprene rubber (0.5mm) Polyvinyl chloride (0.7mm)
Respiratory protection	Particle filter EN 143 or 149, type P2 or FFP2
Eye protection	Safety glasses with protective shields (EN 166)

Personal protection information provided on Kremer MSDS sheets Last updated February 16, 2009.

Important note to reader: There have been recent concerns and discussion regarding the use of the Kremer Zapon stains. The concern relates to the potential of the dye to move through a medium, or migrate, while the solvent remains in that medium. Once the solvent has evaporated, it is unlikely that the dye will then move through the medium. There is also a potential to move the dye through the medium if the solvent has not fully evaporated before layering on top or from later applications of varnish or inpainting that might re-dissolve the dyes. Conservators have typically used the dyes with relatively fast evaporating solvents, such as ethanol. There is also a concern with later removal of inpainting or varnish where the stain would be re-dissolved and potentially discolor porous or imperceptibly porous paint films, both original and recent. Currently, there has been no scientific study directly related to these concerns.

Acknowledgments: I would like to thank Laurent Sozzani for his detailed descriptions of inpainting with the dyes and Carolyn Tomkiewicz for sharing her past experiences with using the dyes as well as her inquiries with Kremer Pigmente regarding the manufacture and use of the dyes.

Christina Milton O’Connell

Submitted October 2008

Endnotes

^{This method of creating a dye palette was described by Laurent Sozzani, Painting Conservator at the Rijksmuseum, Amsterdam. A petri dish can be used for the dye palette because not a lot of color is necessary due to the intensity of the dyes. A ceramic dish with wells can also be used.}

^{According to product literature, the Zapon dyes have not been rated in the CIE or RGB color spaces.}

^{Petria Noble, Head of Paintings Conservation at the Mauritshuis, indicates that her department commonly uses Prussian blue as a substitute for the blue Zapon dye since Prussian blue is a transparent color that more closely matches the blues encountered in 17th-century Northern European paintings.}

^{In e-mail correspondence from 26 August 2008, Eva Eis of Kremer Pigmente described the dyes as 1:2 metal complexes composed of a central atom and two azo molecules.}

^{Lightfastness rating number available in Kremer product literature and online. See Kremer Website}

Additional Resources Consulted

Colour Index International. n.d. www.colour-index.org

Dion, J. 2004. Personal communication. August 10.

Effman. E. 2008. Personal communication.

Kremer. Product literature. Available [1]

Maines, C. 2008. Personal communication. August 19.

Mass, J. 2008. Personal communication. August 26.

Noble, P. 2008. Personal communication. October 5.

Tomkiewicz, C. 2004, 2008. Personal communications.

Whitmore, P. 2008. Personal communication. September 18.

Yoder, D. 1996. Inpainting with Kremer’s wood stain/varnish. WAAC Newsletter: Technical Exchange, vol.18, no 3.