Relative Humidity is the ratio of the partial pressure of water vapor in an air-water mixture to the saturated vapor pressure of water at a prescribed temperature.
Synonyms in English
Relative Humidity (Preferred (Getty Research Institute, 2004)); Atmospheric Humidity;
|Portuguese||umidade relativa do ar|
|Chinese (Transliterated Hanyu Pinyin)||xiāng duì shī dù|
Most organic materials expand and contract as temperature and relative humidity rise and fall. These fluctuations cause unwanted changes to objects, such as splitting and distortion (Landry & Hoag, 2009). High levels of humidity can lead to mold growth. Proper temperature and relative humidity maintenance generally means avoiding the extremes of both.
A relative humidity between 40 - 60% is generally appropriate for most collections, though proper levels will depend on the object's composition (Hilberry & Weinberg, 1994). Mold growth can develop above 70%, and excessive dehydration may result below 30%. A fully integrated heating, ventilating, and air conditioning (HVAC) system regulates both temperature and relative humidity, and is the best aid for creating stable environments. In the event that an HVAC system is not or cannot be put in place, humidifiers and dehumidifiers can help if properly monitored. (Landry & Hoag, 2009). There are a variety of techniques and equipment to help monitor environmental conditions, such as hygrometers or newer electronic systems.
Getty Research Institute. Art and Architecture Online Thesaurus. "Relative Humidity". Last modified 2004. http://www.getty.edu/vow/AATFullDisplay?find=relative+humidity&logic=AND¬e=&english=N&prev_page=1&subjectid=300192097
Hilberry, John D. and Susan K. Weinberg. "Museum Collections Storage," in Care of Collections, edited by Simon Knell, 155 - 175. New York: Routledge, 1994.
Landry, Gregory J. and Robert W. Hoag. "General Care," in The Winterthur Guide to Caring for Your Collections, Gregory J. Landry, et al., 9 - 18. Winterthur: Winterthur Publications, 2009.