While we spoke earlier in this enlightened blog about devitrification (see here), we neglected to tell you what it actually is (Mikey was reminiscing about his long gone mullet obviously...Vanna Opal). ‘Devit’ is a not uncommon problem fusers will suffer from sooner or later- a crystallization of the surface of the glass which like unwanted houseguests is not easy to deal with or as attractive (for an overly simple explanation). Sadly, as in many mother-in-laws, it is not removable. Happily, however, it is treatable.
Moving along, let’s see what we can do to fix it.
As you gaze in wonderment and amazement at this inspiring work of art and skill done by Mikey and Zenia, you might notice that the SP1009SF Black base for this project devitrified badly. Oh, the horror!
But why?
Some possible causes and solutions;
• it’s possible that the Bullseye endorsed glass cleaner caused it. This is the first time we tried this cleaner which smells like a combination of Windex and alcohol. We typically use isopropyl alcohol as a final cleanup after washing our glass with a detergent (alcohol is not very good at cutting through cutter lubricants which are mostly oil-based- another reason we prefer kerosene (yes, it also is an oil, but almost not). Remember, always handle cleaned glass by the edges with oil-free hands.
• Perhaps the SP1009SF Glass was the cause. It was fusible which means that aside from having a known expansion, it is also formulated to minimize devit, but not always and opals are more prone to devit. Multiple firings also could encourage devit. We often purposely dirty up a small sample and do a test firing before investing a lot of time and effort using a glass that might be suspect. If we still want to use a glass that might cause us problems there are options such as capping with clear, sprinkling a thin layer of clear glass powder or overspraying with such readily available products such as Spray A and Borax.
• Did we run a program too long in the ‘devit zone’? This would be temperatures above 1300F. The longer we keep our glass above this temp, the higher the susceptibility it will have to devitrify. Best case scenario is to fire up to between 1000-1250F with a hold of 10-30 minutes and then speed up the firing (500F or more) until you reach your terminal temperature. Of course, there are ranges here- you have to adapt your schedule according to project size and/or thickness.
• Was the ‘air’ in the kiln polluted meaning the kiln and peepholes were closed and unable to vent off any impurities (glue, shelf paper, duck fat)? Some glues are better, some worse at causing devit. One we can heartily recommend is Bullseye’s Glastac, or favourite. Minimize their use or just stop using your glass for roasting dinner...
• Grinding. Working a piece of glass with a glass grinder will almost certainly increase the likelihood of devit. Focusing on good glass cutting to remove the need for a grinder is the best solution as a smooth glass cut edge is best. Second best is to not let your ground pieces dry out by keeping them in a tub of water with some detergent, vinegar (we are Canadian, but that doesn’t mean to use cider vinegar, ok?!) or even grinder coolant to increase the water’s wetness (that’s right- coolant actually does that) and when ready to set up in the kiln, scrub all edges with a toothbrush (Mikey gets a thrill out of using Vanna Opal’s Oral B Ultrasonic toothbrush and not telling her).
• Any combination of the above. This last one is one that we like the best. You see, you might be doing your prep and firing where you are just on the edge of having devit occur but not quite. Then, some minor anomaly occurs (you peek in the kiln because you are just too nosy and impatient thereby usurping the firing schedule, or you missed a fingerprint, etc). One change might have not been an issue, but the two together might have.
So Mikey you ponder, now that I know how to avoid devitrification, how do I fix the piece I made yesterday?
One way of repairing devit involves is by removing the top skin of the glass. Sandblasting, grinding, acid etching- all labour intensive and for most our applications, a little too involved. There is a simpler and equally effective solution and that is to use some sort of top coat to coat your work and thereby 'glazing out' the devitrification. Zenia’s preferred way is to spray coat a thin layer of Spray A (or Borax or other overspray- remember, some may not be food safe as they may contain lead) using a mouth atomizer, and then refiring. Easy, uncomplicated and virtually 100 percent successful. And that's what we did to fix this piece-
In closing, keep in mind that it is more preferable to avoid devit to begin with than it is to have to deal with it after...
