- 1 Guideline 13.1: Materials used in exhibit fabrication and furnishing are known to be object-safe
- 1.1 What hazards can construction and fabrication materials create for exhibit objects?
- 1.2 Which materials are the main sources of pollutants and contaminants?
- 1.3 How can the exhibit team select materials that will not produce contaminants and pollutants or otherwise damage objects?
- 1.4 What materials are the most object-safe choices to use in exhibit construction, and which should be avoided?
- 1.5 What are object-safe materials to use for object labels and exhibit signs?
Guideline 13.1: Materials used in exhibit fabrication and furnishing are known to be object-safe
What hazards can construction and fabrication materials create for exhibit objects?
It is common sense that the materials selected to construct exhibits should be robust enough to support exhibit objects without risk of collapse. However, materials can introduce many other hazards besides the threat of physical damage: Organic materials, such as wood and wool carpeting, can harbor insects and molds; weathered material, such as old barn wood, although appealing for its aesthetic qualities can also produce dirt and dust; wood and synthetic materials can off-gas, introducing harmful levels of contaminants and pollutants to the exhibit environment. Such materials can be especially damaging if they come into direct contact with objects—for example, through being used in object mounts—or through being included in exhibit enclosures where contaminants can become concentrated.
For this reason, caution must be exercised when materials are selected for exhibit furniture and furnishings. In particular, it is essential that non-hazardous materials should be used within a sealed case or when large quantities of a product are used throughout the exhibit area.
Which materials are the main sources of pollutants and contaminants?
Unfortunately, a wide variety of construction materials, adhesives, and plastics commonly used to construct or decorate exhibits have been found to produce damaging pollutants and contaminants as they age and deteriorate.
Damage can occur through direct contact between an exhibit object and a material, for example:
- Fugitive paints and dyes or fluid contents such as oils can transfer from the material to the exhibit object.
- Certain plastics contain additives that migrate, over time, out of the plastic and deposit onto the objects.
- Some materials are chemically reactive when in contact with objects having a particular chemical composition. For example, copper will react with leather in a moist environment and create verdigris.
Or damage can occur through indirect contact when pollutants are carried through the air to the exhibit object. This occurs when volatile organic compounds (VOCs) are emitted from chemically unstable material such as wood and plastics (referred to as off-gassing). Materials commonly used in exhibits that can create pollutants include:
- Wood, which contains both free acetic and formic acid, and generates more acid over time as it ages. When these acids off-gas they are very corrosive to exhibit objects, causing the yellowing and weakening of paper and cellulose, the corrosion of metals, etc. Elevated temperature and high humidity dramatically increase the release of these corrosive gaseous fumes. (The acid in wood can also damage objects through direct contact.)
- Wood products, such as certain types of plywood, also outgas formaldehyde, which is corrosive to objects.
- Paper products that are not archival quality, such as low-quality mat board, produce acids causing paper to yellow and weaken.
- Many manufactured products and materials, such as paints, plastics, and adhesives contain volatile organic substances, including solvents, anti-oxidants and plasticizers, that can off-gas vapors that corrode and weaken objects. Although most off-gassing occurs when a material is new, it may continue throughout the life of the material, sometimes increasing over time as the material deteriorates.
- Fabric: Acidity, and may contain fire retardants [Needs clarification]
- Wool: Emits sulfur (and can also cause damage through direct contact because of its lanolin content).
How can the exhibit team select materials that will not produce contaminants and pollutants or otherwise damage objects?
From a conservation standpoint, it is essential to avoid fabrication materials that are a potential source of damaging pollutants and other hazards. To identify safe materials, whether natural or man-made, the team can consult lists of approved and tested materials from the following sources:
- Published lists of acceptable materials. [link to resources]
- Large conservation facilities such as the Getty, the Smithsonian, and the Canadian Conservation Institute generally publish formally or informally their findings and their testing methodology for the safety of materials.
- The “Recommended Materials List”: The following section provides a list of materials organized into broad categories and identified as “best choice,” “use with caution,” and “avoid.”
- Unknown Materials: To determine the safety of materials that do not appear on any materials’ lists, see Guideline* on researching and testing unknown materials.
What materials are the most object-safe choices to use in exhibit construction, and which should be avoided?
Following is a list of materials organized in a range of categories, including materials used for construction, assembly, and decoration. The best preservation choices are given in each category, along with those materials that should be avoided and those that could be used with caution.
Materials that are not the “best choice” can sometimes be used safely in small quantities in large, open exhibit areas with good air circulation and filtration. A material’s chemical stability is particularly critical, however, when large quantities of a product are used throughout the exhibit space or within an exhibit enclosure.
In general, if a material is labeled as “archival quality” it is appropriate at least for use in short-term exhibits.
Metals possess characteristics that make them a good choice for exhibit construction: Metals typically used in construction do not off-gas and introduce pollutants to the exhibit; they do not harbor pests or contain moisture; and most metals are strong and thus suited for load bearing.
- Best: Aluminum and steel are the most practical metallic building materials because they are commonly used in construction and are plentiful. However other metals and metal alloys are also completely appropriate. Composite metal/resin panels: New metal laminated composite boards are both practical and safe for exhibit construction. A layer of polyethylene is laminated between two layers of aluminum (e.g. Alucabond and Dibond).
- Avoid: There are no metals that must be avoided for construction purposes. (Certain metal wires can react with exhibit objects and should not be used to secure exhibits or labels. [Edit for accuracy.] See Adhesives and Fasteners below.)
Solid wood panels are sometimes used in exhibit construction. However, wood is naturally acidic and off-gasses acetic acid and formaldehyde, both of which can be damaging to objects.
- Best: Tropical hardwoods are relatively impermeable and do not emit large quantities of acetic acid. To avoid contributing to another conservation problem, look for wood that is certified as “Sustainably-harvested” by the Forest Stewardship Council.
- Avoid: Most wood and wood products. Wood contains free acetic and formic acid, and more acid is generated over time. Elevated temperature and high humidity dramatically increase the release of corrosive gaseous vapors (acids and organic compounds) that can be harmful to many objects. Oak, in particular, is a poor conservation choice. Solid wood is expensive and has a low span-to-weight ratio—over long spans its strength is often insufficient and deflection occurs. If wood products are used within the display chamber, they must be isolated with a vapor-impermeable barrier and sealed before being painted.
Exhibit cases, shelving, and furniture are more often made from plywood than from wood. Plywood, both soft and hardwood, is made with one of three adhesive formulations: urea-formaldehyde, melamine-formaldehyde, or phenol-formaldehyde. These adhesives or their additives emit into the air chemicals that have caused damage to a wide range of collections: causing proteins and cellulose to cross-link and become brittle; altering the color of some pigments; corroding metals, especially lead alloys; and promoting the formation of crystals on glass.
- Best: Products made with phenol-formaldehyde, the most stable of the three common adhesive types. Request a phenol formaldehyde bonded hardwood with a hardwood veneer core. A polyvinyl acetate or PVA adhesive is used with hardwood plywood. There is no harmful emission rate. These wood products can be expensive and difficult to locate.
- Avoid: products made with urea-formaldehyde and melamine-formaldehyde.
Wood Composite Boards (particle and fiberboard)
Over the last decades wood composite boards such as particle and fiberboard were often used in the construction of museum exhibits due to their affordability and dimensional stability.
- Best: Specialized Boards. Some manufacturers make specialized boards that do not utilize the more hazardous adhesives. Request formaldehyde-free composite board.
- Avoid: Standard particleboard and fiberboard in exhibit case construction or in close proximity to objects. Most of these boards give off formaldehyde emissions.
Adhesives and Fasteners
Many different glues and adhesive systems have been used in exhibit construction and exhibit assembly. However, whenever possible, the use of adhesives should be avoided. Most adhesives emit large quantities of solvents and un-reacted monomers during their drying or setting phase, which can be corrosive to objects. Even after this initial period, off-gassing can continue indefinitely. Caution must be used when considering the use of any adhesives inside exhibit enclosures.
- Best: For exhibit assembly, use alternatives to adhesives: Fabrics can be wrapped around shelves, pedestals and floor panels and secured with rustproof staples or pins or other mechanical fastenings. [For precautions to follow in use of fabrics, see “Fabrics” section below.] Other attachment methods include hand stitching and archival-quality double-sided tape. For exhibit construction use mechanical fastening such as screws and bolts.
- Use with caution: Acrylic resins, polyvinyl acetate, and high-temperature heat-activated glues. These produce less off-gassing than contact and pressure-sensitive glues.
- Avoid: Contact and pressure-sensitive adhesives; these types of adhesive include some of the most damaging adhesives. Rubber-based adhesives, either vulcanized or synthetic, are poor choices (they do not age well) due to their sulfur and chloride content. Two-part adhesive systems, such as epoxy and polyester types, also have a poor track record for long-term stability. Traditional hide glues are problematic due to their sulfur content, which can damage silver metal, photographs, and other materials. Copper wire can react with leather to create verdigris and should not be used to secure objects in an exhibit. [Edit for accuracy.]
Paints, Varnishes and Caulks
Paint systems, varnishes and caulks contain a variety of chemicals, including ammonia, formaldehyde, sulfur, organic acids, and solvents. They are problematic because these chemicals can off-gas and corrode objects.
- Best : Paints and finishes with little or no volatile organic compounds emissions (VOCs). Choose systems based on water-based acrylic resins with zero or low VOC emission rates. Several major paint manufacturers now provide products that are labeled “zero” VOC.Review the composition of commercial interior finishes to ensure they do not contain components identified as harmful on the “Acceptable Materials” lists. As an added precaution, allow all paints and finishes a full three weeks to cure to ensure any emissions have ceased.
- Avoid: Alkyd or oil-based paints. These off-gas for long periods.
Foams are often used to construct mounts or textile display forms. They are also useful as a cushioning material for mounts.
- Best: Polyethylene foams that are cross-linked with radiation or foamed with inert gas are the most stable types available.
- Avoid: Polyurethane foam products because of damaging off-gassing.
Exhibit designers achieve different decorative objectives by using fabrics to line walls, pedestals, and case interiors. However, fabrics can introduce pollutants into the exhibit environment and can harbor pests.
- Use with caution: Pure cotton, linen, silk, and polyester fabrics are generally suitable. However, all fabrics should be tested before use because they may have been treated with an unacceptable finish or dye. For example, permanent-press cotton is often treated with formaldehyde. Mothproofing agents and anti-static treatments may contain formic and acetic acid. Some of these finishes are water-soluble; therefore fabric should be washed in hot water before use. Washing will also preshrink fabrics and remove excess dyes, which can otherwise transfer to display objects due to accidental wetting or during periods of high humidity. Use a mechanical attachment method or sew fabric to itself; archival-quality double-sided adhesive tape is useful for temporary exhibits.
- Avoid: Wool fabrics (including felts containing wool). Wool emits volatile sulfur compounds that are damaging to silver metal, photographs, and other materials. Wool can also harbor pests.
Both manmade and natural fiber carpet have been identified as a source of unsafe volatile chemicals. While carpet is seldom used inside a case, the quantity used in an exhibit space makes informed decision-making important.
- Best: A cotton fiber with a short nap. If it is unavailable, choose a synthetic fiber such as nylon. Use conservation-safe polyester felted pads.
- Avoid: Wool carpets, which emit volatile sulfur compounds and can attract and harbor insects; All carpets with rubber-based backings, which are often integrated into the base of the carpet fiber; Nylon carpets with a thin, foam backing containing polyurethane.
What are object-safe materials to use for object labels and exhibit signs?
- Vinyl will off-gas
- Paper-based products