A bit of background on devit can help understand how to minimize it.
Most materials are crystalline solids – meaning that all the atoms and molecules are arranged in a pattern. Glass is an amorphous solid – meaning that there is no pattern and every molecule is more or less arranged differently. The literal meaning of word devitrification is to become un-glass-like. ie Put another way, devitrification (devit) is thecrystallization of the materials in glass.
Material can only crystallize when there is a nucleus (think “seed”). In glass, there are two potential sources for the nucleus: contaminants (“dirt”) or the clustering on glass molecules.
The key to minimizing devit is to deny it a nucleus. As glass artists, we have two ways to do this:
1) Clean our glass as well as possible. Anything on our glass that does not burn away 100% can be a nucleus for devit. Oils (from your cutter or your hands) are especially hard to clean off completely. In our studio we never use oil in our cutters (which works just fine). Also, a stiff buffing of your glass with a new, dry, white, and unprinted paper towel typically gets oils off better than using lots of glass cleaner (most of which have oils in them). Printing inks are often petroleum based which is why you should stick to unprinted paper towels.
2) Fire your glass at the lowest possible temperature to minimize fluidity of the glass. The less fluid the glass is, the less molecules can move about and cluster.
Once the process starts it will accelerate – which is why secondary firings always seem to devit more even when we clean our glass well and fire to the same or lower temperature.
My experience is that Bullseye and Spectrum both do an excellent job formulating glass that is devit-resistant – but there is only so much you can do to fight the inherent nature of the materials. Over the years, I’ve come to care less about devit (most of my work takes 4 or more trips through the kiln) and just plan on a step to fixing it at the end of the creation process.
Fixing it, btw, usually means sandblast and fire polish (or slump for a matte finish) OR thin-cap the glass with crystal clear glass powder or Super Spray. It typically adds a firing, but that’s a small price to pay for work with a pristine finish.
Paul
Paul
FusedGlass.OrgHelios Kiln Glass StudioPaulTarlow.com
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