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Causes of Devitrification

Devitrification, a scummy, generally unattractive surface appearance that occurs when glass molecules start to crystallize as they cool.  It usually takes the appearance of a whitish scum on the top edge of the glass being fired. Most glass artists consider it to be a nuisance to be avoided, but some like the effect and use it in their glass projects.

Devitrification has many causes, but here are some of the most frequent.

1.  The chemical composition of the glass -- devitrification is most common in glasses that have a high lime content.

2.  The type and color of the glass -- devitrification is more common with opalescent glasses.

3.  With float (window) glass, devitrification is more likely on the tin side of the glass.  Placing the tin side down against the shelf will help reduce the risk of devit on float.

4.  Improper cleaning of glass before firing is another cause of devitrification.  This is especially true of ground edges and surfaces of the glass.

Coming soon -- more causes of devitrification.

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Copyright 2006 Brad Walker.  All rights reserved.

Thanks to Graham Stone for some of the items in this tip.

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Copyright 2005-2006 by M. Bradley Walker.  All rights reserved.

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