It is important to make sure that storage furniture is made of safe, permanent materials and that its use furthers the care and preservation of the collections it is meant to protect. Furniture has the potential to damage collections both chemically and physically.
Improper furniture materials and coatings can produce byproducts that react to form acids and other damaging chemicals in the presence of moisture and oxygen. These accelerate the chemical deterioration of collections. Furniture that is the wrong size or overcrowded can cause physical damage, including distortion, torn pages, worn or broken bindings.
Some materials commonly used to construct shelving and cabinets can actually contribute to the chemical deterioration of collections.
Wood and wood-composite materials (e.g., plywood, particleboard) have traditionally been used for shelves and cabinets in cultural institutions. Oak and chestnut are extremely damaging woods and should never be used for storage furniture. True mahogany, walnut, and spruce are among the least acidic woods. Although attractive, wood is the least desirable material for storage furniture because it off-gases harmful acids and other substances. Wood-composite materials may also off-gas formaldehyde from adhesives. While some woods and wood composites are less harmful than others, this is only a matter of degree. Even older wood furniture can continue to off-gas damaging acids throughout its lifetime.
If replacing your wooden shelving and furniture is not feasible, there are treatments to minimize the damage. Moisture-borne polyurethane can be used to seal wood, which will lessen the off-gassing effects. There are also barrier products for lining shelves and drawers, made of metallic laminate, glass, or Plexiglas, to provide a layer of protection. Enclosing collection material in archival boxes and folders will also protect against wood’s harmful acids.
Various coatings used on both wood and metal furniture have the potential to damage collections. It is now thought that baked enamel (the coating traditionally used for steel furniture such as library shelving, file cabinets, maps cases, etc.) may give off formaldehyde and other volatile gases if it has not been baked long enough at high enough temperatures. Wood coatings such as oil-based polyurethanes or oil-based paints and stains can also be damaging.
The two most stable materials now recommended for storage furniture are powder-coated steel (which consists of finely divided synthetic polymers fused onto the steel) and anodized aluminum (which is nonreactive and uncoated). While chrome-plated, open-wire steel shelving is also acceptable, the wires may leave marks on unprotected items, and is best for box storage.
Regardless of the materials used, the type and amount of furniture for storing collections has a crucial effect on preservation of the materials. Having enough furniture that is an appropriate size for your space (without being overcrowded) improves storage as well as access, and protects collections against mechanical damage
To avoid physical damage, storage furniture must be able to support the full weight and dimensions of the materials to be stored in it, without overcrowding. Furniture should not have rough surfaces, projections, or sharp edges that might cause damage. All shelves should be adjustable, and bottom shelves should be at least four inches above the floor. Arrange furniture within your storage area so that it allows for easy access and safe movement of collections.
Closed metal cabinets or bookcases provide security and protection from light, but there is the possibility of condensation within the cabinet(s) if the air inside is too humid. As the temperature in the room goes down, moisture condenses out of the air and may cause rusting and/or mold growth. Monitor closed cabinets using a small hygrometer, humidity cards, or a min/max thermohygrometer. Airing out the cabinet periodically will help, as would removing the doors. Condensation can also occur in wood cabinets, although it is less likely.
Compact shelving installations allow more collections to be stored in a smaller space by placing shelving units very close together on tracks. This type of shelving weighs significantly more than traditional shelving, so floor loading (e.g., ensuring that the building is strong enough to hold the shelving) is a concern.
It is important to make sure that items do not extend beyond the edges of the shelves; that a few inches of space is provided between units to assist air circulation and discourage mold growth; and that additional smoke detectors and sprinkler heads are provided in areas with compact shelving.