On Aug 17, 3:12Â*pm, Steve Ackman
wrote:
In , on Sun, 17
Aug 2008 21:19:17 GMT, Bill Browne, wrote:

Lauri brought up fire polishing. Â*I'm wondering how much fire are we talking
about. Â*I'm guessing more than my propane torch can supply.

Â* A point source of heat like a torch will break your
glass. Â*In order to fire polish, you need the entire
piece of to be at least to the strain point, and
preferably at or above the anneal point (~950-1000°F).
Then you can apply a torch to the edge to fire polish
without worrying about thermal shock, ΔT's, or internal
stresses.
Â* IOW, fire polishing is generally done in a kiln.
For your application, I'd think you'd want to fire
polish before doing any carving/etching.

--
☯☯

"Fire polishing" is a term used to refer to a method of producing a
smooth edge by heating the glass in a kiln to a temperature high
enough for the glass edge to soften and smooth out. Clear float glass
would require heating to 1350F and holding at that temperature for 6
to 10 minutes (depending on how smooth it was ground before going into
the kiln).

As was mentioned, it is essential the glass be heated uniformly. It
it isn't heated uniformly, it will crack. Can't do it with a torch
unless the torch is big enough to fan flame over the entire glass
surface.