Crizzling
Archaeological Evidence for Glassworking, Guidelines for Recovering, Analysing and Interpreting Evidence, published by Historic England in 2018, defines crizzling as: ‘A network of fine cracks that forms in unstable glass, particularly post-medieval lead glass.’
"The phenomenon often referred to as ‘crizzling’ is usually associated with vessel glass, and its occurrence in stained glass has not been studied extensively to date. Historically, it was thought that in windows the problem only occurred with green glass, leading to the name ‘green glass disease’, but we now know that is also occurs in other forms of glass. Purple crizzled glass is found in the windows of the nineteenth-century church of St John the Evangelist in the small North Yorkshire hamlet of Howsham." Merlyn Griffiths (York Glaziers Trust)
In the publication 'Conservation and Care of Glass Objects', by Stephen Koob (London, 2006) the process of deterioration is described in a number of stages: Firstly ‘sweating’ or ‘weeping’ caused by the appearance of alkali on the surface as droplets (in higher relative humidity) or as crystals (in lower relative humidity). The glass then becomes cloudy and opaque, as it develops a fine silvery network of cracks, known as ‘incipient crizzling’. The cracks become deeper and the surface of the glass begins to spall away, eventually leading to the fragmenting and disintegrating.
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