What happened?

Patricia O'Neill · Post by **Patricia O'Neill** » Mon Oct 06, 2003 9:07 am

Hi all,

This is the first time it happened to me and I need to understand....

My firing schedule:
300/h to 1150 h10
50/h to 1250 h0
600/h to 1490 h20
and anneal

It works fine for me in my other kiln... this is a new kiln (4th firing) and a new shelf (1st firing). I am thinking that the problem is the new shelf.
I kilned washed as usual and it was dry (more than 2 days in an AZ garage). There was other pieces of glass in the kiln and they are fine (they were on another shelf that was not new).

What do you think? I will apreciate any input.

Thank you in advance,
Patricia

Brock · Post by **Brock** » Mon Oct 06, 2003 9:15 am

It's trapped air between the shelf and the glass. Check your shelf with a level, to see if you have any low spots. If not, pre-fire your shelf hotter than just an air dry. Brock

Patricia O'Neill · Post by **Patricia O'Neill** » Mon Oct 06, 2003 10:30 am

Thanks, Brock!

Brock · Post by **Brock** » Mon Oct 06, 2003 10:38 am

Patricia O'Neill wrote:Thanks, Brock!

You're welcome. Incidentally, this part of your shedule: "600/h to 1490" is the main culprit. If you slow down between approx. 1150 and 1450 these kinds of bubbles are less prone to happen.

Patricia O'Neill · Post by **Patricia O'Neill** » Mon Oct 06, 2003 11:55 am

Which rate would you go from 1150 to 1450?
(for larger pieces, 2 layers of Bullseye 3 mm)

Thanks again.
Patricia

Brock · Post by **Brock** » Mon Oct 06, 2003 12:55 pm

Patricia O'Neill wrote:Which rate would you go from 1150 to 1450?
(for larger pieces, 2 layers of Bullseye 3 mm)

Thanks again.
Patricia

It's hard to say, the only way you can tell you've gone too fast is when . . .

I probably go 100-150 F per hour in that range.

Brock

Patricia O'Neill · Post by **Patricia O'Neill** » Mon Oct 06, 2003 4:56 pm

OK, I'll try that next time... and I check the shelf first.
Thanks again.
Patricia

Steve Immerman · Post by **Steve Immerman** » Mon Oct 06, 2003 5:45 pm

I have several of the same photos of my own from when I once had a warped shelf. Maybe firing slowly through that range may minimize the problem - but my guess is it is the shelf.

Steve

Tim Swann · Post by **Tim Swann** » Mon Oct 06, 2003 9:42 pm

I have had the same problem. I traced it back to moisture in the shelf. Air drying even in AZ did not work for me.

Tim