Once accessioned into the collection, museum objects must be appropriately cared for. New objects may be examined by a conservator and treated for any pre-existing damage. The object is then cataloged by a curator or other specialist with knowledge of the objects importance and history. The object will then be given an appropriate storage location.
Museum storage conditions are meant to protect the object and to minimize any deterioration. This often means keeping objects in a stable climate, preventing exposure to pests, minimizing any handling, and using only archival materials that will not deteriorate or harm the objects. Object safety also include providing appropriate security, and planning for disasters and other threats, and making sure that museum staff are trained in proper handling procedures.
Different types of objects have different requirements, and many museums have specialized storage areas. For example, framed paintings may be stored in racks in one room while unframed paintings are kept in large drawers in another. Some objects have extremely specialized needs. For example, material from underwater archaeological sites may need to be kept wet, and some very rare and badly deteriorated objects require oxygen-free environments.
At any given time, museums display only a portion of their collections. This is often because exhibition requires much more space than storage, and is impractical for the entire collection to be out. Museums may also contain many duplicate or similar objects and find that a few specimens are better suited to display than others. In addition, certain objects, particularly works on paper and textiles, are damaged by light and must only be displayed for short periods of time.
Museum collections are often made up of a variety of materials in a single collection including, but not limited to: canvas, oil and/or acrylic paints, wood, ivory, paper, bone, leather, and textiles. The biggest conservation issue for museum collections is the fluctuations in relative humidity and temperature. Relative Humidity (RH) is a measure of the percentage of saturation of the air.
Temperature is not as important to the life of a work of art, but it is true that chemical reactions occur faster at higher temperatures. However, a museum must take into account the comfort of its staff and visitors and it has been widely accepted that 68°F-75°F does not cause a lot of problems for most artifacts and is comfortable for most humans.
It has also been internationally agreed upon that the RH should be set at 50%–55%. This has become widely accepted because the lower limit was set at 45% since damage to organic materials begin to occur below this point. The upper limit is placed at 65% because mold flourishes at 70% RH. It is also cheaper for most institutions to maintain 50% RH rather than 45% or 60%. There is some exception when it comes to tropical climates since the indigenous artifacts are acclimated to RH levels higher than the “museum norm”. Changes can be made to a museum’s RH to accommodate the changing seasons, but they must be made gradually. Humidity should change in 2% per month increments (an increase in 1°F will affect a decrease of about 2% RH).