Tempered float glass is one of the easiest types of recycled glass to come by (after bottles, of course) There are often tempered glass shelves and/or table tops at thrift stores, lots of them on the local classified ads and your local glass shop probably has quite a few that were mis-ordered that they might be willing to give away.
Tempered glass is float glass that has been cooled extremely fast in a controlled environment to purposefully induce extreme surface tension. This is the same kind of tension we are trying to avoid when we anneal our art projects, but it does have its uses.
Once tempered glass gets scratched, it becomes a bit less stable, sometimes it even breaks, and that’s why people want to get rid of the old stuff. Lucky for us, we don’t care if it’s scratched, or even already broken, as long as it’s clean.
To make this bowl, I’ve used a tempered glass shelf, cleaned it and wrapped it in paper. I use a spring loaded center punch to break the glass, it’s a handy little tool for less than $10 and makes breaking tempered glass super easy.
Notice how the glass breaks in long thin strips near the strike point and then changes to smaller squares towards the outside edge. Think about how you can use those long pieces for design elements.
Next I have a prepared mold, I’m using a wide shallow bowl that has been kilnwashed. You can use molds with steeper sides, but it becomes more difficult to stack in the glass, so try and find a nice balance.
Now start filling up the mold with the tempered glass pieces. You can carefully break the larger pieces into smaller ones if you need to. Even though it’s nominally ‘safety glass’ the edges are still sharp.
It’s important to fill up every space. The glass is flat, and the dish is curved, so, as you fuse it, the glass will bend down into the curve and pull in on itself. If you leave big holes between the pieces, they will become even bigger holes after fusing.
Notice how I varied the direction of the long skinny pieces, it’s fun to play with as a design element.
Now, into the kiln it goes, to be fired to a full fuse. If you are using a steeper sided mold, you need to adjust the top temperature down, otherwise the glass will slide down and pool in the mold.
See how there are holes between the pieces that were very hard to see before the piece was fired. And here it is out of the mold. There will probably be some small sharp points that will need to be carefully cleaned up with a file or a grinder. And, although you can’t see the tiny break lines when the plate is in the mold, they are still visible, giving the plate an icy glacial look.