Interior Paints for Exhibit Cases
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The selection of paints used in exhibit cases is an important conservation decision because of the high level of emissions produced by most commercial paints. Systems based on water-based acrylic resins with zero or low VOC emission rates are recommended.
Why are paints a conservation concern?
A paint system generally consists of a solution composed of pigments, a binding medium and a solvent (or vehicle). In the past, paints have been selected with little scrutiny as to their contents and possible effect upon materials being displayed within the case. Today, any solvent-based paint used in close proximity to exhibit objects is considered problematic due to the harmful effects of volatile organic compounds (VOCs) given off by these coatings. Objects are not safe unless a low (or zero) VOC product is chosen. Direct contact with any painted surfaces is not recommended due to the possible transfer of components and the acidic nature of many paint systems.
- VOCs are substances that contain carbon and evaporate readily. VOCs that are harmful to objects include aromatic hydrocarbons, such as benzene and toluene, and chlorinated hydrocarbons, such as methylene chloride. Nitrogen oxides and sulfur compounds are not VOCs but are also emitted into the atmosphere. Either alone or in association with VOCs, they contribute to a range of current or potential atmospheric pollution effects, like ozone depletion, the greenhouse effect, and acid rain. The interaction of sunlight with emitted VOCs can form ground level ozone.
- The measurement of the coating's VOC level is a good way to determine whether the paint is safe to use in an exhibit case. A low or zero VOC content is desirable, and is measured in "grams of VOCs per unit volume.
- The U.S. Environmental Protection Agency regulates levels of VOC emissions in paints (Section 59.402 of the Federal Register. VOC contents are tested by the EPA's Reference Method 24). Paint labels display the "grams of VOCs per liter." The specific definition is "grams per liter excluding water or exempt compounds, thinned to the maximum thinning recommended by the manufacturer," Vol. 61, No. 171, September 1996, Proposed Rules of the Federal Register. A rule of thumb is the stronger the smell of paint fumes, or the higher the gloss level, the higher the VOC content.
|Low VOC Paint Levels||Metric||English|
|Non-flat paint||0 - 150 g/l||0 - 1.25 lbs/gal|
|Flat paint||0 - 50 g/l||0 - 0.42 lbs/gal|
What paints can be recommended for use inside exhibit cases?
There are some general considerations to follow in choosing a paint.
- Solvents and additives: Avoid paints with aromatic hydrocarbons, some of the most damaging VOCs. Research and inquire about other additives which may be present in paint such as mold retardants.
- Resin type: Oil and alkyd-based binders in paints are not appropriate for use inside an exhibit case. Latex paint is more breathable, has better color and mildew resistance, and expands and contracts with wood more easily than an alkyd paint.
- Barrier effectiveness: Neither alkyd nor latex paint creates an effective vapor barrier coating for wood products. Their film is permeable to wood offgassing and formaldehyde emissions. Use latex paint over a specifically formulated barrier coating, foil or laminate.
Acrylic latex paints (emulsions) are dispersions of pigments in a liquid continuous phase of water and an acrylic resin, prepared by emulsion polymerization. Latex water-based paints with acrylic binders are essentially solvent free and are therefore among the safer paints for use within cases. Latex paints are variable, however, and may contain ammonia, sulfur or other undesirable chemicals. Selection and application of a paint should include the following considerations.
- 100% acrylic latex paint has proven successful in meeting restrictive conservation standards.
- Paint loaded with calcium carbonate offers some benefits when acidic materials are a particular concern.
- Paint loaded with titanium dioxide will absorb UV light.
- Remove objects from the painting area during application.
- Never place objects inside the case until the paint is thoroughly dry to the touch and a curing time of at least three weeks has elapsed.
- Be aware that water-based acrylic latex paint can become tacky during periods of high humidity; isolate collection objects from painted surfaces.
- Although they do not provide a barrier to volatile emissions from the wood, shellac and other air-drying lacquers are acceptable clear coatings. Some plastics and resins or gasket and caulk products may react with the alcohol in shellac.
Zero or Low VOC Recommended Paints
The commercial paints in the following table meet the "Green Seal" standard for VOC levels and prohibited ingredients according to Green Seal Inc. Newsletter August-September, 1998.
|Manufacturer||Product Name||VOC Level G/L|
|Benjamin Moore||Pristine Flat||26|
|Benjamin Moore||Pristine® Eggshell||23|
|Benjamin Moore||Pristine Semi-Gloss||18|
|Con-Lux||Enviro-plex Flat White||0|
|Duran||Genesis TM Flat||0|
|Duran||Genesis TM Semi-Gloss||0|
|Duran||Genesis TM Gloss||0|
|ICI Dulux Paints||Lifemaster TM 2000 Eggshell||0|
|ICI Dulux Paints||Lifemaster TM 2000 Semi-Gloss||0|
|ICI Dulux Paints||Lifemaster TM 2000 Flat||0|
|PPG||Speedhide Wall Flat||19|
|PPG||Speedhide Enamel Eggshell||2S|
|PPG||Speedhide Enamel Semi-Gloss||14|
|Sherwin Williams||ProMar 200 B3 I W200 Series Semi-Gloss||37|
|Sherwin Williams||HealthSpec TM BS Series Flat||0|
|Sherwin Williams||ProMar 200 B30 W200 Series Flat||19|
|United Point Mfg.||Aladintone Satin||41|
|United Point Mfg.||Pointers Choice Eggshell||46|
|United Point Mfg.||Parade Flat||12|
|United Point Mfg.||Coverall Flat||14|
|Benjamin Moore||Fresh Start Exterior Primer||31|
|ICI Dulux Paints||Lifemaster 2000 Interior Primer||0|
|Sherwin Williams||PrepRite B28 W300||S0|
|Sherwin Williams||PrepRite 200 B28 W200||26|
|Sherwin Williams||HealthSpec B11 W44||0|
|Sherwin Williams||PrepRite Anchor-Bond BS1 WS0||18|
|United Point Mfg.||Adhere-it (WB) Primer-Sealer||44|
|United Point Mfg.||Acrysheen Primer-Sealer||34|
|United Point Mfg.||Canyontone Water Base Primer-Sealer||39|
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.
- For specific VOCs, consult the U.S. Environmental Protection Agency (EPA) Code of Federal ,Regulations (CAR) Title 40, Part 60 Appendix A.
- Green Seal Inc.
Tétreault, J. Sustainable Use of Coatings in Museums and Archives – Some Critical Observations. e-Preservation Science, 8, 2011, pp. 39-48.