bisque/float glass question

[archie]

Morning from BC

Can I get opinion(s) on the following
12" square of float over a treated bisque form and used the following firing sche in my skutt:

370' ph to 1100
9999' ph to 1325
soak for 14mins ( was fine at this point , that I could see)
9999' ph to 950
150'ph to 750
500' ph to 0000

when I opened the kiln this morning the plate was in about 3 large pieces and a couple small, the edges where deff sharp, have the bandaid to prove

should I take it hotter?, soak?

thanks, archie

[Bert Weiss]

Morning from BC

Can I get opinion(s) on the following
12" square of float over a treated bisque form and used the following firing sche in my skutt:

370' ph to 1100
9999' ph to 1325
soak for 14mins ( was fine at this point , that I could see)
9999' ph to 950
150'ph to 750
500' ph to 0000

when I opened the kiln this morning the plate was in about 3 large pieces and a couple small, the edges where deff sharp, have the bandaid to prove

should I take it hotter?, soak?

thanks, archie

Archie

You have 2 problems with your process. The most important key word is "over" a bisque mold. Glass shrinks more than bisque so the glass will crack every time as it shrinks, hence the sharp edges. Over works on stainless steel or plaster/silica.

Your other big problem is that 950 is much too cool a temp to anneal float glass. Stone recommends a short soak at 1030 and a long ramp down to 945. I soak longer at 1000 and take that same amount of time to go to 900. We spend a similar amount of time.