Devitrification Can Be Avoided By
Taking Some Simple Steps

Some fusing glasses may be more subject to devitrification than others.

It can be caused by contamination on the glass surface. Always ensure your glass is completely clean prior to fusing in the glass kiln.

The most likely cause is that the glass has been too long in the pre-molten temperature range; this is about 1300 F (700 C).

The objective should be to move the glass through this range quickly, either to the glass fusing temperature or down to near the annealing point.

"Crash cool' by venting the kiln from the fusing temperature down to just above the annealing zone.

Before fusing many glass artists apply a "devit spray" (overspray) to the glass, it can be either sprayed or brushed thinly across the surface. This spray protects the glass during the fusing cycle.

You still need to have clean glass and a satisfactory firing schedule.

Dry completely before placing in glass fusing kiln.

It is possible to repair some devitrified pieces by lightly sandblasting.

Sandblasted pieces need to be perfectly clean before placing back in glass kiln. Any sandblasting medium left on the glass will cause the problem to reappear.

You can apply a few coats of overspray to minor damage and re-fire up to around 1425 F (774 C), do not hold at this temperature but drop back through you normal cooling and annealing fusing schedule.

Using diamond hand pads, pumice stone, or a rotary brush may also remove the rough patches on your glass. Follow this with a few coats of overspray and then fire again as per the above.

Bullseye Glass recommend that where a problem occurs on a flat surface, sift a thin layer of Clear glass powder across the glass until the surface appears white.

Fire the kiln to 1425-1450 F (774-778 C) for about ten minutes depending on the kiln and glass thickness, this should give a clean appearance.

Whatever method you use the appearance of your item may change.