Wednesday, 18 June 2014

Slowing the Rate of Advance


The question is sometimes asked whether the rate of advance in a firing schedule should be slowed when re-firing; for a fire polish for example.

Cynthia Morgan contributes four circumstances where you would want to slow the rate of advance:
1) On the previous firing you were fusing a whole bunch of little pieces into a much thicker piece, so you need to reduce your ramp to avoid thermal shocking the thicker glass
2) You think you might not have annealed the piece well enough on the previous firing, so you're playing it safe
3) You suspect there's a crack somewhere in the piece (from cold working or whatever) so you're reducing the chance it will expand quickly and open the crack
4) You've got to do something to the glass/kiln at a certain point in the firing cycle, and if you go at your normal rate you'll wind up doing it at 3AM...so you slow down the firing and get more sleep.

Otherwise, well-annealed is well-annealed. If none of those four conditions obtain, I don't see why you'd need to slow down”.