Preventive Conservation: Storage and Exhibit Materials
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Lead coins in a wooden storage tray. Acetic acid from the wood has caused the lead to corrode. Some of the coins have exploded apart.

Although it may sound strange, pollution can be a major cause of damage to museum collections. The most common form occurs when specimens and objects are housed in containers, including exhibit cases, made of unstable materials. For example, wooden cabinets or exhibit cases give off acids that will cause specimens to deteriorate. Similarly boxes, trays, envelopes and paper used to hold and package specimens can be responsible for damage if they are made of unstable, acidic materials, as seen here. Therefore, we are systematically replacing all inappropriate cabinets, drawers, trays, boxes and packaging materials with ones known to be made of inert, stable materials.

Old wooden storage cabinets (above) in the Peabody are being replaced with new steel cabinets (below) to protect the specimens.

Acidic index cards sitting on this glass plate negative have damaged the photographic emulsion on the negative.

 

Because most paper and cardboard are acidic, direct contact with specimens and objects will cause discoloration and structural damage. Similarly, most plastic bags, containers and foams are made of unstable plastics that give off volatile substances. Acids and these volatiles cause discoloration, oxidation and other forms of deterioration.

 Japanese inro made of lacquered wood, ivory and lead. The lead on the chair atop the elephant and around the edges of the blanket on its side is covered with white lead corrosion products.

 

Pollution can also be a problem in exhibits if display cases are made of inappropriate materials. Woods give off acids and other harmful volatile substances, as do some paints and gaskets around panes of glass. The corrosion on this inro was caused by acetic acid vapors given off by the oak used to construct the exhibit case in which the inro was displayed.

Tibetan silver water container covered with black corrosion products. Sulfur given off by the rubber backing on carpeting used in the exhibit case reacted with the silver to cause the corrosion.

Egyptian mummy mask (YPM29702). After reshaping the mask, a support mount was constructed out of muslin and polyester stuffing (left) to provide support for the mask (right).

 

Over the years, some specimens have lost some of their structural integrity and become quite weak. Others were always fragile and not able to support their own weight. Many specimens therefore cannot be just put on a shelf in storage. Without proper support, they will sag, warp and break.

Support is provided by a structure called a support mount. These mounts are carefully designed to support the specimen and distribute its weight evenly. Some keep objects upright, like this Egyptian cartonnage mask, so that they do not get crushed. Even heavy dinosaur bones need support. Plaster cradles support the bones evenly so that they don’t break.

 Inert polyethylene foam (above) and acid-free tissue and cardboard (below) are standard materials for packing and supporting specimens.

 

Collections staff are careful to use only packing and storage materials known to be acid free and inert. Only foams and bags made of polyethylene and polypropylene, and acid-free tissue, paper and cardboard, are recommended for use with collections. Although these materials are more expensive, their use ensures the long-term preservation of the specimens.