STANDARD 19: Modifying and Maintaining the Exhibit Climate
STANDARD 19: Modifying Exhibit Climate
Effective measures [design, controls and policies] must maintain object-safe climatic conditions that fulfill the Conservation Requirements
OR: The exhibit design must provide exhibit objects the required climatic conditions
Inappropriate relative humidity (RH) and temperature are both damaging to objects. Relative humidity is also directly affected by temperature because, as temperatures rise, RH generally goes down (the warmer the air, the more water it can contain); as temperatures fall, RH goes up. Consequently, fluctuations in temperature will also cause fluctuations in RH. Because of this relationship, RH control should be conducted in tandem with temperature control.
Inappropriate RH can create a host of problems for organic materials, causing them to disintegrate and discolor, to buckle and tent, to shrink or swell. Some minerals will hydrate or dehydrate when exposed to inappropriate RH, and metals containing salts can corrode. Damp conditions (over 75% RH) cause molds, which stain and weaken organic and inorganic materials. Fluctuations in RH can also be damaging. Collection objects exposed to excessive or rapid cycles in humidity can suffer a range of physical, chemical, and biological damage. Composite artifacts (made from two or more different materials) are most at risk from RH fluctuations because the materials from which they are made will react to RH changes at different rates and to different degrees and will pull or push at each other as they shrink or swell.
Temperature affects the rate of most chemical deterioration processes, which doubles for every increase of 18F (10C). Organic materials, especially those that are chemically unstable (e.g., acidic paper, color photographs, nitrate and acetate films) will disintegrate and discolor if temperatures are too high. In fact, most materials decompose gradually at room temperature, although the time scale for complete destruction can be in millennia. Some materials, such as plastics, photographic emulsions and rubber-based materials, become soft or tacky at higher temperatures. While other materials, including paint and other polymers, become more brittle and are easily damaged by handling or physical stress at low temperatures.
Temperature fluctuations can also cause a range of physical, chemical and biological damage in collection objects. Such fluctuation can cause fractures and delamination in brittle, solid materials, especially if they are layered. Dramatic and rapid changes in temperature can cause condensation and thermal shock to inorganic materials such as glass and enamels.
Temperature and RH can be brought to acceptable levels through the use of controls and hardware. Exhibit design and museum procedures can be used both to eliminate sources of damaging temperature and RH within the museum environment and also to ensure that the controls function as intended.
Guideline 19.1: Technological controls that maintain a stable relative humidity are included in exhibit design when necessary
- What are the main controls available for controlling relative humidity?
- What conditions should relative humidity controls aim to create?
Guideline 19.2: Technological controls that maintain a moderate temperature are included in exhibit design when necessary
- What conditions should temperature controls aim to create?
- What are the main types of control for temperature?
- How can exhibit cases be used to provide exhibit objects the appropriate climatic conditions?
- What role can exhibit design play in protecting objects from inappropriate climatic conditions?
- How can architectural modifications aid environmental control?
- What policies can assist in protecting objects from inappropriate climatic conditions?