Hi Jane -Most soda lime
Hi Jane –
Most soda lime glass (Bullseye, Spectrum, window and bottle glass) can bend just north of 1000°F. The reason we slump at higher temperatures (usually) is that the glass needs to soften more so the weight of the glass is enough to cause it to bend.
With the exception of Pebeo style, most enamels and paints meant for firing will need to go higher than 1000°F. The question of if the glass will bend will depend on the shape of the glass, how quickly it softens and just how hot you have to go. For example, a short tumbler can probably go hotter without distorting than a martini glass where a lot of weight is supported by a single stem.
Helios Kiln Glass Studio