Recently we started attempting to slump deep pieces. We have learned the following thru the effort.
1. If you go too hot, the weight of the walls sliding down the surface will cause big huge burstable air pockets.
2. Elevate the ceramic slump mold so that the air trapped underneath fused glass can escape out, if not, it will also trap an air pocket which will raise up and create a large air blister.
3. For deep slumps, you must go slow. See picture below:
The image shows that the middle section of the fused glass disc melted through, got thin and then started dripping and pooling. The needle points on the edges of the fused glass piece show that the glass got too hot and then dragged along the surface. The highest temp was 1240. Moral of the story… ITS TOO HOT. I was also going from 1100 to 1240 at 15 per hour. I read to slow it own it 50 per hour.
I have a top element skutt kiln. I am trying this again using 100 per hour and dropped from 1240 with a 15 minute hold to 1200 with a 20 minute hold.
The piece we are using this time around is very thick about 1/2″ and it has already been slumped once so it has a little slump happening already.