Fused glass pieces are rarely fired only once.
In the case of this frit-stretched bowl, higher-than usual, initial temperatures were employed, as many stacks of glass, and a glass dam were necessary for the technique used. The thickness of the piece required a very slow firing schedule, to avoid shock and breakage. Then the piece was taken to the saw and grinder to cold-work, or shape the edge. Because the edge became rough from the cold-working, and because it was so thick from having been dammed, it was returned to the kiln for second, full-fuse firing. Glass, in its liquid state, wants to "pull" or "spread" to a thickness of 6mm. The dam used in the initial firing prevented that. Then it went back to the kiln a third time, over a bisque mold, to achieve it's shape in a medium-temperature "slump" firing.
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