Guideline 13.3

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Guideline 13.3: Objects and materials selected to create interpretive settings do not introduce agents of deterioration into the exhibit environment

What risks can exhibit props and materials pose to objects?

Chemically unstable materials such as plastics can off-gas or react with exhibit objects causing physical deterioration, corrosion or staining. Organic materials may harbor pests that could infest other organic objects on exhibit. Poor quality or unstable materials can deteriorate thus introducing abrasive dust and particulates. This potential for damage increases when the materials used are close to, or are enclosed with, a collection object.
Through awareness of potential pitfalls, the exhibit team can create settings that exclude such sources of damage to objects. A conservator is trained in material science and can advise on suitable products, suggest alternatives, and identify problems.

What basic precautions should be taken when utilizing props and materials in exhibit settings?

Following are basic guidelines to minimize risks to objects:

Use chemically stable materials that will not react with exhibit objects or create pollutants:

• Avoid materials with high levels of outgassing or other contaminants unless the choice of other materials would be historically inaccurate. For example: oak timbers, unpainted boards, or wood shavings; or rubber-based plastics in adhesives, molded products or flooring materials. [Add content - Provide categories of materials to avoid]
• Pay special attention when using inert casting resins, plastics and foams [Add content - Provide names of materials to avoid]
• Do not use large amounts of unstable polyvinyl chloride or polyurethane
• Identify the additives in a product, including plasticizers and surface finishes that may be harmful.
• Know the compatibility of materials, for example animal pelts should not be used as a display surface for silver objects since fur contains sulfur, which corrodes silver.
• Wash any dyed material, since dyes can be unstable or migrate. If washing is impractical, isolate the material from the collection objects with a physical barrier or a mount.
• Reduce the amount of material needed by using inert fillers such as blocks of polyethylene foam, or by building a platform on which the material can be laid.

Use sturdy materials that are strong enough to hold up under their anticipated use. Flimsy construction could threaten objects or disrupt the exhibit because of the need for refurbishment. And materials that deteriorate can create a source of abrasive dust and particulates:

• Use materials that have structural integrity. Architectural features that support collection objects must remain vibration-free.
• Choose materials rated for heavy traffic that can be replaced in sections. Choose carpet squares rather than wall-to-wall coverings as flooring material along visitor pathways. Choose squares of imitation pebble stone instead of a continuous length of consolidated pebbles.
• Avoid dried and friable materials. Materials such as thatch, shingles and moss may become brittle, creating dust and debris.

Use materials that are clean and sterile. Dirty materials can introduce dust and debris that will deposit on objects and recirculate through the HVAC system:

• Screen and/or wash materials. For example, wash pebbles and sand to remove fine particles, dirt, and insects.
• Use materials free of corrosion.
• Do not use old materials in poor condition
• Ensure materials can be kept clean. As a practical matter, work out methods for cleaning displays before making a final decision on what materials and products to include. Substitute alternative materials for those that are difficult to clean.

Avoid highly flammable materials.

• Follow all fire and life safety codes. Plastics, woods, fabrics and other materials used in exhibits must conform to National Fire and Protections Agency standards.

Avoid organic materials or use with extreme caution. Animal products, wool, feathers, fur, vegetal matter, wood, and preserved foods may introduce pests or molds into the museum. Building materials such as wood boards, thatch, unfinished timbers and composite boards are also a potential source of infestation.

• Flooring materials, including dirt, sand, pebbles and earth can also introduce pests.
• Use reproduction botanical models, such as silk or wax replicas, to avoid the problem. Original natural history specimens must be pre-treated before inclusion in exhibits.
• Use freeze-dried vegetal materials where possible.
• Inspect ALL materials for infestation before bringing them into the museum.
• Fumigate or freeze organic material before introduction, if in doubt. This kills eggs and larvae. (Mobile truck freezers can be utilized on site.)

Ensure materials are completely dry. Moist materials can corrode or stain adjacent collection objects. Moist botanical materials can also deteriorate and support mold growth.

Always isolate prop materials from the collection. Because prop materials can introduce a range of hazards to collection objects, such as moisture and acidity, abrasive surfaces and migrating chemicals, they should not be allowed to touch exhibit objects.

• Use protective barriers. Polyester films (such as Mylar), polyethylene sheeting, and tailor-made mounts can be used to isolate collection objects from a prop.
• Enclose loose material to prevent transfer to other areas and to discourage vandalism; for example, place polyester netting over vegetal material to help contain the small particles. Cover friable materials such as thatch, sand, and shredded plastics with fine polyester netting.

Ensure materials used to create special effects are object-safe. All naturalistic effects, such as weather and water, should be simulated with object-safe synthetic materials. For information on how to create naturalistic effects, see following sections.

How can water and weather effects be achieved safely in exhibits?

Following are basic guidelines to create object-safe water and weather effects in exhibit settings:

Water effects:

Never use water in exhibit settings: A water reservoir elevates relative humidity in the surrounding area and increases the likelihood of mold growth; pumps are also likely to malfunction, and drains often clog.

Achieve water effects in settings and dioramas with non-hazardous synthetic materials:

• Plexiglas and Mylar create a convincing illusion of water at a low cost.
• Use pourable resins that are stable over time. Acrylic resins are preferred. Allow enough time for the plastic to cure before introducing non-collection objects.

Weather effects—snow, ice, rain, and fog:

Use the most stable resins and plastics: acrylics, silicones, polyethylene, polystyrene, and polycarbonate.

• Never apply any resin to an accessioned collection object or to an item that will be hard to replace.
• Allow these materials to cure and off-gassing to dissipate before introducing collection objects.

Pourable resins can be used to imitate snow, ice, and rain. These include clear acrylics and clear or opaque silicone rubbers.

• Add a bulking agent such as fumed silica to white silicone rubber to give the right consistency.
• Never allow these materials to touch collection objects.

Plastic-based shredded materials can imitate snow.

• Limit the build-up of electrostatic charge by using glass glazing rather than plastic glazing, and wood or tile flooring rather than carpeting. [Should wood be sealed?]
• If possible, cover the material with fine netting.

Use thin coatings of resin to imitate ice or snow.

• Use forms molded or shaped of wood, papier maché, blocks of polyethylene, or other materials to give depth to displays. This allows a thin coating of resin or other material to provide the appearance of ice or snow. [And the coating prevents the wood from off-gassing?]

Use dry ice (solid carbon dioxide) or liquid nitrogen to recreate fog. There is no documentation that these materials harm collections, as long as they do not touch objects. However, both depress the temperature of the surrounding air.

• Locate the reservoir away from collections.
• Do not use the effect near collection objects that are temperature or humidity sensitive.

What precautions should be taken when using taxidermy specimens in exhibits?

Taxidermy specimens are important elements in environmental displays and are also found in historic rooms. However, they may harbor pests and contaminants:

• Inspect specimens routinely for infestation or deterioration.
• Treat, or dispose of appropriately, any specimens showing signs of infestation.

Special precautions must be observed when using freeze-dried specimens: While conventional taxidermy (a skin is stretched over a form) is preferred in most situations, sometimes freeze-dried specimens can be used in displays. Freeze-drying has the advantage of preserving a realistic appearance on small, delicate specimens. It is also a relatively inexpensive process. However it is a far less reliable form of preservation than conventional taxidermy and should not be used on large specimens or for long term exhibits. Freeze-dry preparation should be used only when all of the following conditions are met:

• Sealed exhibit cases will be used
• Ambient humidity levels are likely to be moderate to low (below 55% RH)
• Visitor contact will not occur
• Specimens are small (i.e., squirrel and smaller; small reptiles, amphibians, song birds, etc.)
• Specimens have low fat content
• Freeze-dried specimens will be isolated from collection objects with a layer of polyester or other impermeable sheeting. Fats and oils from the specimens may migrate, and contamination from deteriorating specimens can stain other materials.
• Freeze-dried specimens will be routinely monitored and disposed of at the first sign of decomposition.

[Link to NPS Guidelines] Commissioning taxidermy specimens see Guidelines, T.N. ___
[Link to NPS Guidelines] Safe use of non-collection props within an exhibit, see Guidelines T.N. 1:10
[Link to NPS Guidelines] Creating safe food and plant props in exhibits, see Guidelines T.N. 1:11

Incorporating food and plants into a display presents several conservation challenges. Careful selection of artificial materials and monitoring are important to prevent damage to collection objects. For more information, click link.