You know how you know something that is just fundamental to what you do. And then you forget to think and do the math and alas, whatever happens is your own fault. I know that fused glass likes to conform to 6mm or 1/4″ and I think I have even mentioned this in a blog before. If you fuse a piece that is less than this thickness, it tends to pull in on the sides as it is trying to get to that magic thickness. If you fuse a piece that is greater than this thickness, it then rounds itself out a little as it melts down to reach that magic thickness.
I recently made a piece in which I first created a part sheet out of Bullseye stringers on a piece of 3mm clear and then wanted to combine this with other sheets of glass. So the part sheet went in the middle and then I added 3mm pieces on either side of the striped part sheet. But the part sheet seemed to be about 2mm higher, so I decided to add clear 2mm on top of the other colors to get everything to the same thickness.
Okay, do the math. 3mm + 2mm does not equal 6mm!!! Yes, I know the rule. When I pulled the piece out of the kiln, you can see where the pieces pulled in on either side of the part sheet to try to reach that magic 6mm thickness. (Sorry, but I forgot to take the picture until after I started to cut it up and did so quickly. You can still see where the crack was on either side, the crack on the right side being much longer. And you can tell I did some editing to make the photo better – sorry.)
Since I had another part sheet, I tried again and this time did the math. I added an additional 3mm clear sheet across the entire piece: 3mm + 2mm + 3mm equals 8mm, which resulted in some rounding (you can see this slight rounding in the picture) and needed to sand the edges to get it back to a rectangle again. I could have used a 2mm clear sheet, but the 3mm piece was already cut when I did the math.
To try to save the first piece, I cut the piece apart into 3 pieces along where the cracks were, sanded them flat and then reassembled, added a 2mm sheet of clear under the entire piece, and refired. Not bad for a fix-up.
Of course, I have to end here with a completed piece, so here is the final red striped plate!