I recently got a Paragon SC View (or SC2 - View) and have been exprimentally cooking various kinds of glass. I've found that opaque and iridescent glasses used to construct "regulation" stained glass pieces tend to devitrify.
From these boards I've learned to keep temps below 1400, but am also interested in the Borax solution often mentioned. Is there a set Borax:water ratio?
Mix approximately 1 tsp. of borax to 1 cup distilled water.
Shake to mix. If any borax remains undisolved, decant the solution to remove those crystals. Add a drop or two of dish soap or TSP to act as a surfactant to keep it from beading on the glass. It works like a sticker spreader to help with the application.
I use cheap plastic sprayers to apply Borax. Since it will inevitably go out of solution and crystallize inside the spray mechanism, I run clean water through it when done, and next time it's ready to go. Also easy to put bottle part of sprayer in microwave to get the solids mixed back in.