You open the kiln expecting a glossy fused piece and instead find a dull, hazy, scummy film on the surface. That's devitrification, or "devit," and it's one of the most common frustrations in glass fusing. The good news: it's almost entirely preventable once you know what causes it.
Devitrification is crystal growth on the glass surface. When glass is held too long in a certain temperature range, tiny crystals form and scatter light, turning a clear glossy surface cloudy or rough. It's not dirt and you can't wipe it off; it's a structural change in the surface.
| Prevention | Why it works |
|---|---|
| Clean glass spotless before firing | Dust and fingerprints are seed points for crystals |
| Ramp fast through the devit zone | Less time in the zone = less crystal growth |
| Cool quickly back down through it | Devit forms on the way down too |
| Use anti-devit spray or clear overcoat | Adds insurance on long firings / sensitive colors |
Clean your glass. A thorough wash and a lint-free wipe before every firing prevents the majority of devit, because those tiny crystals need a starting point, and dust or a fingerprint gives them exactly that. For long firings or colors you know are prone, a light coat of anti-devit spray is cheap insurance. And rely on a well-tested schedule for your specific COE so you move through the danger zone efficiently.
You can often rescue a hazy piece by applying an overglaze or anti-devit spray and re-firing, or by fire-polishing. It's not always perfect, but it beats scrapping the work.
A controller that ramps precisely through the devit zone makes this problem mostly disappear. I'll help you pick the right glass kiln. Spencer — (801) 839-5882.
{"one"=>"Select 2 or 3 items to compare", "other"=>"{{ count }} of 3 items selected"}