Yesterday, one of our new customers sent me this picture. Have you experienced this bubble problem? I did! Nearly 20 years ago, before I started using Kaiser Lee Board as a kiln shelf.
Here is my reasoning behind the bubble issue. Glass is a very slow heat conductor, while clay is a very good heat conductor. For example, you can hold a 3″ long glass stringer into a candle flame and it won’t get hot at the end of the stringer, even after softening in the front. With a clay piece, you would burn your fingers in no time. (If you want to try the clay part of this experiment, please have some Pepto Bismol next to you, to treat your burn marks).
When you place your glass on a clay shelf, there is always some air between the glass and the shelf and while the kiln heats up, the air gets hot and since it can’t escape will blow a bubble into the soft glass. Kaiser Lee Board, on the other hand, does not conduct heat any faster than your glass. In addition, it is also porous and any trapped air can escape easily. Another advantage of fusing with Kaiser Lee Board is that you can fire a lot faster than with clay type kiln furniture. Oh yes, I have read about all the tricks and hoops you have to go through to avoid those bubbles and Kaiser Lee Board.