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I am fusing 2 pieces of 3mm Bullseye white glass and it isn't fusing completely flat (slight concave up). It's a problem because I have to glue the top layer of the glass to a metal base. I dont know why it's not fusing flat. The piece is 5" x 1". I fuse 400 DPH to 1000. Then AFAP to 1390 and hold for 2 minutes, then AFAP to 960, hold for 1.5 hours, and then 75 DPH to 750, and then turn off. I'm stumped why it isnt fusing flat. If anyone has any ideas, I'd be most appreciate.

Thanks!!

Put a hold in at 1100 on the way down. Tim

Higher temp and/or more time at the top.

Marty wrote:Higher temp and/or more time at the top.

Agree with Marty. Especially with white.

There are various reasons why glass might warp. A simple one that can't be fixed is a compatibility issue where the top and bottom layers are contracting at different rates. The only thing you can do there is configure it differently.

I have seen glass warp when there was a gap between bricks in my kiln wall. I closed the gap, refired, and it flattened out.

Check to make sure your kiln shelf is flat, a lot of the inexpensive ones are not.

thank you all for your comments. All great ideas, which I will try. I can't fuse it to too high of a temp because I can't have the pieces round out too much. But perhaps a little higher temp will work. And I will check to make sure my kiln shelfs are flat. And try to hold at 1100 on the way down.

Bert, when you say to configure it differently, not sure what you mean. If I have to fuse 2 sheets of white glass, I'm not sure how I can configure that differently.

Thanks!!

AJK25 wrote:thank you all for your comments. All great ideas, which I will try. I can't fuse it to too high of a temp because I can't have the pieces round out too much. But perhaps a little higher temp will work. And I will check to make sure my kiln shelfs are flat. And try to hold at 1100 on the way down.

Bert, when you say to configure it differently, not sure what you mean. If I have to fuse 2 sheets of white glass, I'm not sure how I can configure that differently.

Thanks!!

2 sheets of the same glass will not create a warp from differing COE's. 2 sheets of differing glasses could. Encasing the higher COE piece with 2 sheets of the lower, would fix that. You could use thin sheets for that.

If one piece contracts more than another in a 2 sheet stack, it will suck in and create a warp. These glasses could easily still be in the range of compatible, so nothing cracks, it just warps. If you were to cut or break the fused glass, the warp would change.

i'm fusing sheets of the same glass and same COE, so there shouldnt be any issues there (if I understand correctly).

AJK25 wrote:i'm fusing sheets of the same glass and same COE, so there shouldnt be any issues there (if I understand correctly).

The one time I had a warp, it was with a single sheet of 10mm thick float glass. The problem was caused by too big a gap between bricks that surround my kiln. I refired it with the bricks placed back together and it went away.