Glass disease
Glass disease, also known as sick glass, is a degradation process encountered in art conservation. Glass disease is caused by an inherent fault in the chemical composition of the original glass formula. Usually, inadequate calcium oxide causes the alkalis in the glass to remain water soluble at a low level. Exposure to higher levels of relative humidity during storage or display causes these salts to hydrate and leach out of the glass. Upon a reduction of relative humidity, these hydrated salts can then form a crust on the surface. This process causes a complex disintegration of the glass which can be identified through a variety of symptoms. One such sign is the aforementioned crusty deposits which can form a visible hard alkaline coating on the surface. Another symptom is a distinctive network of fine cracking, also called crizzling, which can reduce the transparency of the glass or even threaten the integrity of the structure.
References
Citations
Appelbaum, Barbara (1991). Guide to Environmental Protection of Collections. Sound View Press. ISBN 0-932087-16-7.