I know this is an old one, but I have started a new series to my work of fused glass bowls and plates that are quite involved to produce and the glass color base plates on some of them bubble and some do not. I have used glass frit under the base color on top of the main circle. I have left air space at the ends, I am using a slump speed only, no first fuse and it is coming out much better, but still there are unwanted bubbles on every 4th plate. Can anybody help????