Safe and Harmful Materials for Use in Exhibits

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The stability of materials used in close proximity to collection objects, including the materials used to build exhibit cases, is an important conservation consideration.

Are some construction materials safer to use in close proximity to museum collections?

Research and experience has shown that some materials are more acceptable for use in close proximity to museum collections. These materials are non-acidic, non-outgassing, and chemically and physically stable. The first chart in this TechNote lists materials implicated in the unnecessary deterioration of museum collections, and the second list suggests those considered to be more acceptable.

Materials To Avoid	Pollutants
Woods • oak • sweet chestnut • Douglas fir • yellow pine • red mahogany (Khaya) • teak • western red cedar • cork	acetic and formic acids; organic peroxides
Wood-bonded products • masonite • chip board • particle board • interior plywoods bonded with urea formaldehyde • C grade plywoods	formic acid from adhesives; acetic and formic acids and peroxides from wood
Papers • Unrefined wood pulp papers and cardboards	organic acids, peroxide, sulfur
Plastics • polyvinyl chloride • polyvinylidene chloride • bubble wrap • cellulose nitrate • cellulose acetate , cellulose diacetate, cellulose triacetate (most stable in group)	hydrogen chloride and plasticizers hydrogen chloride and plasticizers polyvinyl chloride used in adhesive nitric acid variable–acetate group can evolve acetic acid
Rubber (vulcanized natural or synthetic)	sulfur
Foams • polyurethane • low molecular weight polymer sponges • polyesters (generic term; variable; may be under-cured)	organic acids; acetates
Paints • oil • oil modified (alkyd, tung oil, tall oil, in mineral spirits, oleo-resinous) • latex (styrene butadiene, polyvinyl acetates, vinyl acrylic emulsion with lithopone pigment)	fatty acids, sulfur, hydrogen peroxide, aldehydes, fatty acids, sulfur ammonia, fatty acids, sulfur, hydrogen sulfide
Waxes and Plasticine	fatty acids, sulfur
Varnishes • polyurethanes • oil based • latex	variable, formic acid, organic acids, fatty acids
Adhesives • protein-based glues (animal) • rubber-based or plasterized • cellulose nitrate • polyvinyl acetates (especially low molecular weight) • urea formaldehyde adhesives	sulfur sulfur nitric acid acetic acid formic acid
Fibers • wool, animal fur, semi-tanned skins and leather • nylon 6 and nylon 66 • permanent press and crease -resistant fabrics • flame-resistant fabrics • pest proofing • fabric's dyed with sulfur dyes	sulfur sulfur formaldehyde formaldehyde formaldehyde sulfur

Materials shown to be more appropriate for use in exhibits

Selection of exhibit construction and finishing materials should be drawn from the following list which is taken from the current conservation literature.
Woods

Well seasoned, air-dried spruce, mahogany, walnut, basswood, poplar, balsa

Exterior grade plywood bonded with phenol formaldehyde or non-formaldehyde emittin glue

High-density or medium-density boards using formaldehyde-free adhesive; e.g., Resincore I Medite II Medex

Paints (require aeration/thorough curing and isolation from direct contact with display objects)

Acrylic latex: test each brand and color before use; aerate cases at least three to four weeks before object installation

Shellac: aerate case at least two to three weeks before object installation

Two-part epoxy resins; 100% solid precisely mixed

Plastics

Polyacrylonites: e.g., Plexiglas, Lucite

Polyethylene: non-chemically polymerized Polypropylene

Polycarbonates

Polystyrenes: variable

Polyester: variable- e.g., Mylar D which is polyethylene terephthalate

PTEF tape

Foams

Polyethylene: e.g., Volara type A; gas expanded foams such as Plastazote

Adhesives (require aeration/thorough curing)

Acrylic polymer solutions (e.g., Acryloid B-72)

Wheat starch pastes

Methyl cellulose

Polyvinyl acetate emulsions, neutral pH adhesive; may evolve acetates and acidic acids— aerate case thoroughly before object installation

Double sided archival tape; e.g. 3M 415

Hot-melt adhesives: e.g., Thermogrip 6330, Evo-Stik 7702

Caulking (requires aeration/thorough curing)

Silicon-based sealants without ammonia, such as RTV (Room Temperature Vulcanized)

Mechanical fastening methods

stainless steel or monel alloy staples and pins; sleeve pin mounts with inert tubing

Fabrics

Vegetable fiber cloths: cotton, linen; wash with hot water before use

Polyesters

Acrylics

Papers

Acid-free pH unbuffered (neutral) paper products (for use with photographs and protein-based materials such as silk, wool, semi-tanned skins, leathers)

Acid-free buffered (alkaline reserve) papers (for most other materials)

Products, Manufacturers, and Suppliers

Mention of a product, manufacturer, or supplier by name in this publication is for information only and does not constitute an endorsement of that product or supplier by the National Park Service. Listed materials have been used successfully in past applications. It is suggested that readers also seek alternate product and vendor information to assess the full range of available supplies and equipment.

Additional References on the Subject

Arni, P.G., G.C.Cochrane and J.D. Gray. "The emission of corrosive vapors by wood".

I. “Survey of the acid-release properties of certain freshly felled hardwoods and soft woods.” Journal of Applied Chemistry, l5 (l965): 305-3l3.

II. “The analysis of the vapors emitted by certain freshly felled hardwoods and softwoods by gas chromatography and spectrophotometry” Journal of Applied Chemistry, l5 (l965): 463-468.

Blackshaw, S.M. and V.D. Daniels. "The Testing of Materials for Use in Storage and Display in Museums." The Conservator, 23 (l979): l6-19.

Brady, George S. and Henry R. Clauser. Materials Handbook. 12th Edition.New York: McGraw-Hill Book Co., (1986).

Carpenter, J.M. and P.B. Hatchfield. Formaldehyde: How Great is the Danger to Museum Collections? Center for Conservation and Technical Studies, Harvard University Art Museums, Cambridge, MA. (l985).

Craddock, A.D. "Plywood as a Storage and Display Case Material." Textile Treatments Revisited. Harpers Ferry Regional Textile Group Preprints, Washington, DC (l986): 40-46.

Fitzhugh, E.W. and R.J. Gettens. "Calclacite and Other Efflorescent Salts on Objects Stored in Wooden Museum Cases." Science and Technology, R.H. Brill, Ed. MIT Press, Cambridge, MA. (l97l): 9l-102.

Hawley, Gessener G. The Condensed Chemical Dictionary. 10th Edition. New York: Van Nostrand Reinhold Co., 1981

Hodges, Henry. "Show Cases Made of Chemically Unstable Materials." Museum. 34: l (1982): 56-57.

Hopwood, Walter, R. "Choosing Materials for Prolonged Proximity to Museum Objects." AIC Preprints Seventh Annual Meeting, Toronto, Canada (l979): 44-49.

Leveque, M.A. "The problem of formaldehyde - a case study." AIC Preprints Fourteenth Annual Meeting, Chicago, IL. (l986): 56-65.

Miles, Catherine. "Wood Coatings for Display and Storage Cases." Studies in Conservation, 31 (1986): ll4-l24.

Oddy, W.A. "An Unsuspected Danger in Display." Museum Journal, 1 (1973): 27-28.

Padfield, D.E. and W. Hopwood. "Trouble in Store." Science and Technology in the Service of Conservation. IIC Congress, Washington DC (l982): 24-27.

Tennant, Norman H. and Thomas Baird. "The Deterioration of Mollusca Collections: Identification of Shell Efflorescence." Studies In Conservation, 30 (1985): 73-85.