Firing uneven layers requires more care than a piece equally thick all
over.
My rule of
thumb is to add the difference between the thick and thin to the thick and fire
for that. So, a piece with a 6mm base and a total height of 12mm gives a difference
of 6mm added to 12mm gives a firing thickness of 18mm. If you look up the
bullseye site annealing for thick slabs, follow the schedule for 19mm. The
initial heating rate can usually be half the final cooling rate shown in the table.
The
Bullseye recommendations are more conservative.
They recommend that the firing rate should be for something twice the thickest
part of the piece. In this case, the
firing would be for a piece as though it were 24mm. Again, the initial rate of
advance would be equal to half the final cool segment in the Bullseye table
Annealing Thick Slabs.
If you are
slumping a thick piece, you can use the initial rate of advance all the way to
the slumping temperature and then anneal according to the thick slabs table.
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