Dangers to malacological collections: Bynesian decay and pyrite decay

Abstract Specimen deterioration in museum collections and exhibits is a recurring worry of curators. Malacological collections, i.e., those containing mollusk shells, are of special concern, because these specimens are composed largely of calcium carbonate, a compound that easily deteriorates in acidic storage media. There are two main problems related to the presence of volatile acids in collections: Bynesian decay and pyrite decay. In Bynesian decay, acetic and formic acids, among others, are released by the materials used to store the collection: wood, varnishes, resins, paper, cardboard, and other storage materials. Under high relative humidity and inappropriate temperature, the acids react with the shells' carbonate, yielding salts and carbon dioxide. Pyrite decay is similar in appearance: fossil specimens may contain pyrite (FeS2), which in high relative humidity is oxidized, yielding sulfuric acid and other products. This acid corrodes other shells, including carbonatic fossils. The damage caused is irreversible, but there are methods to avoid or mitigate it. The collection should be kept in conditions of low relative humidity (45–50%) and appropriate temperature range (16–21°C). The use of archival materials, such as steel drawers and cabinets with electrostatic coating, is mandatory. Specimens containing reactive pyrite must be kept in archival-quality plastic containers or closed glass containers. Damaged specimens must be immediately removed and only returned to the collection after proper cleaning.