Efflorescence appears as a powdery or crystalline crust on the surface of objects such as stone, plaster, or ceramics.
Bloom, deposit, encrustation, cementation
Efflorescence forms as a result of water migration and subsequent evaporation. Efflorescence that typically forms on masonry surfaces, mural paintings, and frescoes occurs when moisture dissolves water soluble salts, then migrates to the surface, leaving a visible salt residue (Getty Research Institute, 2004). Efflorescence growth can result from an inherent vice of the object - migrating water reacts with an object's chemical makeup or extraneous deposits (Demeroukas, 2010), as well as fluctuations in water vapor pressure that occurs with changing temperature and humidity.
The first indications that efflorescence is be occurring in an object may be the appearance of a white haze on the surface, indicating any soluble salts present are crystallizing. Eventually, the object surface or even the object's body itself will begin to crumble; over time, the object could be reduced to a pile of dust (Little, 2000). This type of physical deterioration can be catalyzed by extremes or fluctuations in temperature and relative humidity. Preservation measures include maintaining a stable environmental temperature of 68°F (+/- 3°) and a relative humidity of 50% (+/- 5%), or by removing the soluble salts through desalination treatment.
Demeroukas, Marie. "Condition Reporting," in MRM5: Museum Registration Methods, edited by Rebecca A. Buck and Jean Allman Gilmore, 223 - 232. Washington, DC: The AAM Press, 2010.
Getty Research Institute. Art and Architecture Online Thesaurus. "Efflorescence". Last modified 2004. http://www.getty.edu/vow/AATFullDisplay?find=efflorescence&logic=AND¬e=&english=N&prev_page=1&subjectid=300214748
Little, Margaret A. "Glass & Ceramics," in The Winterthur Guide to Caring for Your Collections, Gregory J. Landry, et al., 57 - 66. Winterthur: Winterthur Publications, 2009.