Shelf?

[wordana]

Could it be the shelf? If it is uneven (has “dips”), these will cause air pockets, that will cause bubbles, that will cause holes.

 

This is assuming you are using at least two layers of glass — if you are using 1 layer, the glass is too thin and causing holes.

Dana W.

Jester’s Baubles Fused Glass Designs

http://www.jestersbaubles.com