Glass fusing is heating and softening glass in a kiln to join two pieces or two sides of a bottle together. Slumping uses molds to bend and shape fused glass. Most pieces I make are fired once to fuse and flatten it, and then fired a second time to shape it. The entire process generally takes days to complete. Here are some other things people often ask and some pictures of the glass at various stages as seen through the peephole on the side of the kiln.
Do you smash or press the bottles?
They actually melt flat on their own. Liquid glass naturally wants to be ¼” thick*, so if you get it hot enough for long enough, it will melt until it reaches that thickness. By watching through the peephole in my kiln, I can actually see when the glass is completely flat (or when it has slumped enough to be a bowl).
How hot do you have to get the glass?
The temperature varies greatly from kiln to kiln and based on how flat you want the bottle. I like a really flat bottle, so I heat them to about 1500 degrees.
How do you keep the glass from breaking?
The secret is annealing, which is strengthening the glass and reducing its brittleness by controlling the temperature drops. Both when you heat up and when you cool down the glass, you have to change the heat at a slow even rate, usually somewhere between 70 and 300 degrees per hour. That means it can take 14 hours or more to simply “melt a bottle.”
How do you cut shapes from a bottle?
Cutting shapes from a bottle is a several day process because I first have to make flat pieces of glass to work with. First, I cut a bottle into four segments, and then I fuse the middle segments flat in the kiln. Then I use a saw or a glass cutter and a grinder to cut shapes from the flat pieces. Finally, I fire these pieces smooth in the kiln or fuse them onto another pieces of glass.
*I know that glass doesn’t WANT anything, but really… because of a bunch of technical stuff like density and surface tension, liquid glass evens out at about 1/4” thick.