Devitrification is a major problem on bottle slumping. Some means of reducing the problem are
- clean labels off thoroughly
- remove all adhesives
- scrub the whole bottle and polish dry
- apply a devitrification spray before firing.
- Spend as little time in the devitrification range (700C – 750C) as possible
- Vent the kiln up to 540C if you are using fibre papers
- sandblast off the devitrification and fire again if the devit is slight
- in severe cases of devitrification, throw the bottle away.
Champagne and large bottles of sparkling wine split easily due to the differences in thicknesses. Firing of these needs to be very slow until you get past 715C.
Bottles with printed labels need particular care. The enamels used in the printing may contain lead and any other elements in the paint may contaminate your kiln.