A friend gave me a 12" steel ring about a 1/2" in height . I lined it with fiber paper and filled in my glass and fired 450 dph to 1550 hold 140 min
ramped down & annealed . I still have the small popped bubble look on top.
and this baby is thick a tad over 1/4" I need to refire to loose the popped bubbles and add more color [to much clear] 250dph to 1600 / 1650?
some hold times in here? and to make a short story long, how can I add a rim + clear blank when this dang thing is already pretty hefty. can you thin down a blank without having it all over your kiln? and would kiln wash not fiber paper make the edges not so spiky... I did keep it away almost 1/2" from the edges and still got monster spikes... *sigh*
Since you are casting in a steel ring you have to have the fiber paper. It works as a cushion so that the ring doesn't get trapped. It shrinks more than the glass.
If you just want to fill the bubble holes I would just add clear frit and do a regular fuse. I have never re-done a high fire to add more color so can't really advise you there. Your high fire temp seems a little low as well. I high fire at 1700F
The nature of the high fire beast is that you have to cold work it after, because of scummin or needles or kiln wash or whatever.
a slightly over 1/4" thick blank isn't going to grow much larger. you can figure it out by weighing it and then calculation. glass weighs 1.6 lbs/sqft. the rest is left as an exercise to the reader.
if you put a rim around it, it has to be double thickness. if you do this before you refuse, then the center blank will creep under or between the two layers of glass. it won't flow on top of the rim.
a tad over 1/4" I need to refire to loose the popped bubbles and add more color [to much clear] 250dph to 1600 / 1650?