Annah James wrote:Bert:
So when Brock says to go to 1510 degrees, I shouldn't? I could take it to a lower temp and hold it longer...will it devit? (The piece is warped, not bubbled, by the way - about 1/2" tall in the center...)
I am holding off the next firing until I feel like I have SOME understanding of what I am dealing with here...oh my.
Also, one of you talked about putting the tin side up. How do you tell??
sheepishly - I 'thought' I knew how to fuse glass....
Annah
You find the tin side with a UV light. Search the archives; there's tons in there on this. And the tin side should be down, not up.
I would like to see the element layout of your kiln. How many elements are in the wall compared to the ceiling? This isn't a big, coffin Olympic glass kiln is it? My guess is that the warp is partly a function, again, of the edges of your glass being hotter than the center. The middle of the three panels had more even heat so it didn't thermal shock, but your ceiling element isn't hot enough to get the glass up to the same temperature as the edges. You could both baffle the wall elements and raise your shelf so it is closer to the ceiling elements. Also, slow down a little at the top temp.
An aspect of firing that you should understand is that glass "sees" the IR, (Infrared Radiation); it is effected more by IR than other forms of heat, such as the temperature of the air in your kiln. Any glass that is openly exposed to a glowing element is going to get hotter and softer faster than any glass that can't see the element. Glass that is closer to an element that it can see, gets hot much, much faster than glass further away, just like a piece of paper is illuminated much more as it is brought closer to a light bulb. (That's because the IR is spreading out into three dimensional space as it radiates away from the element.) Ceramics, on the other hand, can't "see" the IR. That's why you can load a ceramics kiln with pots inside larger pots and many shelves of pots stacked above and below each other, and all the pots will bisque the same. If you baffle the wall elements of your kiln, you will hide the glass from their IR and even out the temperature of your glass.
Another way to simplify this whole process is to settle on a set soak at whatever top temperature you are fusing or casting at. Is an hour hold at 1465 the same as 20 minutes at 1520? Who knows? I can say for sure that an hour at 1465 is less than an hour at 1520. In a class I took with Ted Sawyer, head of research and education at Bullseye, he soaked everything the same amount of time.
ch