The length of firing time for glass sagging is less than ceramics. Place an 015 and 014 cone in your kiln in a pat of clay and fire until the 014 is halfway down, turn off the kiln and cool slowly.
If you want to retain the shape of a glass piece that has been painted, you should not fire it above 022 as the glass will soften and distort above this temperature
If you would like to try sagging glass, one thing to remember is that your shelves and kiln must be level. If not, your glass will not be symmetrical.
If you have over-fired glass, the edges will have needle points and the finish will be dull
When painting glass such as bottles, use the same loading and firing procedure as you would for overglaze
You can fire glass and ceramics at the same time as long as you use the proper temperatures for each item.
Glass sagging involves placing of a piece of glass such as a sheet or a bottle in a mold and heating it until the glass softens and takes the shape of the mold.
When sagging glass in a mold be sure to dust the mold with whiting or some recognized separation agent or the glass will stick to the mold.