fusing shattered tempered glass pieces Q

[Nancy Conrad]

I doubt this is an original idea (although my searches have not found similar info) and would appreciate any tips from those who have tried this!

I want to use pieces of shattered tempered glass (safety glass?) to make pieces about 12-15" in diameter that I will then drop slump.

I have done some tests--small pieces work well, one 8" square piece seemed to fuse well, but when I tried slumping, it broke in several large pieces (total of 5 pieces). Since I was testing, I was using my 8" kiln, so I wonder if not enough air space around the edges (i.e. it was almost touching the edges) would cause the breakage or another reason.

I'd like to add some color & tried sprinkling small amounts of bullseye frit inbetween 2 layers of chunks. It looked good after fusing, but broke when slumped.

all ideas welcome!--much thanks for this resource of information!

[Bert Weiss]

I doubt this is an original idea (although my searches have not found similar info) and would appreciate any tips from those who have tried this!

I want to use pieces of shattered tempered glass (safety glass?) to make pieces about 12-15" in diameter that I will then drop slump.

I have done some tests--small pieces work well, one 8" square piece seemed to fuse well, but when I tried slumping, it broke in several large pieces (total of 5 pieces). Since I was testing, I was using my 8" kiln, so I wonder if not enough air space around the edges (i.e. it was almost touching the edges) would cause the breakage or another reason.

I'd like to add some color & tried sprinkling small amounts of bullseye frit inbetween 2 layers of chunks. It looked good after fusing, but broke when slumped.

all ideas welcome!--much thanks for this resource of information!

It sounds like the glass broke on reheat from heat shock.

Bullseye glass is not compatible, won't work. For color, you can get frits from CR Loo or you can roll the frits in enamels by various companies like Ferro, Paradise, etc. The enamels are opaque in thick application so you risk deadening the glass. The frits from Loo are nice though.

I have a glass blower make me colored float frit by remelting the float glass with a small addition of cobalt or copper oxides. When he gets the recipe right it is beautiful and compatible. He simply dumps the hot glass back in to a bucket of water and it frits up. I just made a countertop with some of this. I don't like the process of crushing and sizing the glass though. Glass dust sucks.

Bert

[Tom White]

Nancy, Your immediate problem seems to be one of thermal shock. When glass is heated it expands in size, when it is cooled it decreases in size. If it is heated unevenly it expands unevenly. It sounds like you are working in a kiln with elements in the side walls of the kiln, not in the lid. If this is the case and the edge of your glass is very near the elements of your kiln it is most likely that the glass was heated much faster at the edges of the piece than in the center and the resulting difference in temperature produced enough stress in the glass that it split it apart.

Check the tutorials on the home page of this board for the basic information about fusing and slumping glass. Brad's book, available in the online catalog link has a lot of information it too. Read the tutorials and if possible get a copy ot the book to gain a better understanding of how glass reacts when it is heated.

Best wishes,
Tom in Texas