How do you slump glass bottles in a ceramic kiln?
Most kilns can slump glass bottles. Wine bottles are a fairly easy project. You don't have to worry about glass compatibility, since you are not fusing different glasses together. (If different types of glasses are fused together, they must be compatible, meaning they must expand at the same rate. Otherwise the piece will crack.)
I saw a slumped glass bottle for the first time in 1984. Frances Darby, who founded Paragon, was experimenting with glass, because we were introducing our first glass kiln. After the kiln cooled, she took out a kiln-washed, ceramic bisque bowl with a bottle slumped inside. She was experimenting to find out if kiln wash could be used as glass separator. "It works!" she said.
Though we knew little about firing glass back then, that first bottle experiment was a success. That's how easy slumping bottles can be.
Use glass separator to protect the shelves from the glass. (Kiln wash also works.) Place the glass onto the shelves, or on molds designed for bottle slumping. The molds will require small holes so that air can escape as the glass bends. At the slightest cracking or peeling of separator or kiln wash, apply a fresh coat.
You must be able to see the glass as it bends. You should position the bottles so you can see them through peepholes. Shut off the kiln when the glass has bent to the degree that you want. As a starting point, you could fire a bottle to cone 016.
Cooling usually must be slow from 1100 degrees F. to 700 degrees F, which is the annealing range. The smaller the project, the faster the glass can cool through that temperature range. Small earrings, for example, can be taken out of the kiln and left on the shelf within 15 minutes after fusing. Cast glass, on the other hand, takes days to cool.
If the glass cracks, slow down the firing and cooling.