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
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
Copyright 2006 Brad Walker.
All rights reserved.
Thanks to Graham Stone for some
of the items in this tip.