Fw: [ATM] Slumping

[richas at earthlink.net (Richard Schwartz)]

Advice on annealing and slumping is in my web page and has been posted
there for a long time.   

However, here is what you need to know:

Slumping will be done in a half hour at 640degC.   Before slumping, heat
the glass to 600degC for an hour, then to 620degC for a half hour.   Then
bring it up the final 20 degrees for slumping.   After a half hour, you can
crash cool the kiln to 550degC by opening the door.

For plate glass, the critical temperature range is from 550 degC down to
375degC.   Above or below this range you can heat or cool the glass as fast
as you like.   In the critical temperature range, I cool at a constant
rate.   The time required for the critical 175 degC drop fron 550 to 375 is
60 hours per inch of thickness (24 hours per cm.).   To be absolutely sure
of getting stress free glass, add the thickness of the slumping form to the
thickness of the glass.  You will save a lot of anneal time with a thin
slumping form!

Below 375degC, you can cool at four times this rate without breaking the
glass.

Caution: if the glass is warm when you take it out of the kiln, PUT IT
BACK, even if it is very comfortable to hold in your hands.  Warm glass in
cold air is a good way to get a crack.  If the bottom of the glass feels
warmer than the top, PUT IT BACK until everything is at room temperature. 
Final cooling can be with the kiln door open to speed things up.

This works well for me.   It is not my intent to contradict or offend any
experts whose advice is more credible than mine.  Do check your glass with
polarized light to be sure it is annealed properly.

. . . Richard


> [Original Message]
> From: Vladimir Galogaza <vladimir.galogaza@zg.tel.hr>

> Therefore I thought that receiving information on proven and working
> procedure, proven on ATM blanks, will be the shortest and cheapest way to
> get some results.
>
> Unfortunately I received no help from those who know it for sure.
> It seems that you are right that :"mistakes will be a learning experience
."
>