Collections Care
Conservation is a fundamental responsibility of the National Museum of American History (NMAH) and an essential element of the museum's mission.
Our role in collections care and exhibit design is focused primarily on practical techniques that protect museum collections from damage caused by exhibit, handling, and storage.
The NMAH conservation department handles preservation concerns throughout the entire process of exhibit development and production. Conservation specialists also monitor and offer recommendations on environmental conditions in both public and storage areas.
The Conservator of Exhibitions and Loans coordinates conservation treatment and advises on exhibit guidelines for loaned collections, ensuring that both incoming and outgoing loans are properly cared for at every stage of the loans process.
Changes in temperature, relative humidity, and light impact collection materials in a variety of ways. Some materials are sensitive to a single environmental condition. For example, most metals corrode in humid environments, meaning they can weaken or even wear away. However, metals are rarely affected by the light or temperature in a museum environment. Other materials, like wood, might expand and contract with changes in both temperature and relative humidity. And some artifacts, like those that are textile-based, are sensitive to all of these environmental factors.
Environment
Temperature
Temperature, in many cases, is directly related to how quickly a material will degrade. Generally, materials last longer at lower temperatures. High temperatures increase how quickly materials degrade. Extremely low temperatures can cause some materials to freeze, become brittle, or shatter. Temperature in the museum environment is kept as constant as possible to prevent rapid changes, which might damage or weaken a variety of materials, particularly plastics, waxes, and applied coatings.
Relative Humidity (RH)
Relative humidity is expressed as a percentage and is the amount of moisture that the air can hold before reaching dew point, the point at which water in the air condenses to form liquid water. High relative humidity can cause some materials to mold, swell, or warp. Low relative humidity can encourage materials to dry out, shrink, crack, or flake. Frequent changes in relative humidity weaken most materials and can increase the rate of degradation. The NMAH monitors both collection storage and galleries to ensure optimal relative humidity levels are maintained throughout the museum.
Light
Light is a source of energy that interacts with everything. Fortunately, it is the most controllable environmental factor for collections housed indoors. Bright light is more damaging to collection objects than dim light, and sunlight is more damaging than electric light. Learn more.
Lighting is an especially important factor in both exhibit design and collection care. Most of the time, light damage builds up and is permanent. When the museum is closed, the lights are dimmed or extinguished to protect collections on view in the galleries. The museum controls external light through common devices like window shades, curtains, and screens. Lighting engineers ensure that artificial light is maintained at acceptable levels for collection objects on view in the museum galleries.
Case Construction
A well-designed exhibit case controls the environment inside it, called the microenvironment, so sensitive artifacts can be exhibited safely within. All case materials within the enclosed volume of the case are non-reactive; they have been tested to ensure that they are safe for use in a sealed environment with collection objects. If necessary, conservators might add substances called scavengers to a sealed case. These substances absorb pollutants and slow unwanted chemical reactions. Dataloggers are often placed inside sealed cases and allow collections staff to monitor the environment within. Silica gel and other desiccants, or substances that absorb moisture, are used to maintain optimal humidity levels.
Custom case designed for Dorothy's ruby slippers
Housing
Collection housing is the joint responsibility of conservators and collection managers; it includes everything from the container in which an artifact is stored to the environmental controls of the room in which that container is kept. When collections are not on view in the galleries, they are placed in collection storage where they can be referenced, researched, and safely maintained. Conservation staff must test and approve all housing materials.
Integrated Pest Management (IPM)
The NMAH's IPM program is a preventative, long-term method of controlling pests without toxic chemicals. The Smithsonian's Museum Conservation Institute (MCI) created a checklist for museums looking to implement an IPM strategy.
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