Over the last 10 years museum curators and librarians have begun to realize that humidity is more important to preserving rare works of art and priceless antiques than is temperature. As a result, specifications have been changed to require proper humidity control in museums, and particularly for roving exhibits.

When King Tut visited the United States, every showing of his artifacts was required to be held in a humidity controlled environment. More recently the same was required for a roving

exhibit of American pioneers who "won the west".

If you take wood from outdoors that has equalized with the outside air moisture content, into a heated building with a lower moisture content, the wood will begin to give up its moisture to the dry air in the building. As the wood loses moisture from its edges, the edges will shrink and pull apart creating cracks, or warping the wood. This same damage can occur with paper, textiles, some plastics, wax, porcelain, fruits and vegetables and other materials that have the ability to absorb or give up moisture. Such materials are said to be hygroscopic (water absorbing). Hygroscopic materials always seek to reach equilibrium with their environment.

In the case of a museum, where expensive paintings, books, sculptures and other hygroscopic materials are kept, rapid changes in Relative Humidity can be devastating and will eventually destroy the artifacts. In a printing operation, paper that is rapidly drying while running through a press, will shrink and curl causing jamming, tearing and even misregistration of printing colors. In a microchip wafer fabrication laboratory, slight changes in the dimension of a Silicon wafer can result in chips that are not usable.

The key to protection of hygroscopic materials is stability of the environment. It is detrimental to permit the Relative Humidity to vary rapidly or widely throughout the year. This is one of the reasons why control (or stabilization) of the Relative Humidity is becoming an important part of Indoor Air Quality. This is accomplished by dehumidifying when the air becomes too moist and humidifying when the air becomes too dry.

Carel USA is proud to provide systems to protect our heritage and insure that these artifacts will be there for our

children.

• The National Archives (The Constitution, Declaration of Independence)
• George W. Bush Presidential Library
• Houston Museum of Natural History
• The Smithsonian Institution
• The National Galleries

Important Links regarding preservation of:

Special Collections: http://aic.stanford.edu/library/online/brochures/objects.html

Furniture: http://aic.stanford.edu/library/online/brochures/furn.html