Chalks can be used to draw on glass, and are compatible with COE 90, COE 96 and even float glass. They must be fired to cure the piece, so that the added design doesn't come off. Use chalks on the top or bottom surfaces of glass. All chalks are food safe and lead free, 3/8" round x 3" long. 14 assorted colors per pack.
Since the chalk won't stick to smooth glass surfaces, we recommend either crushing up the chalk and "painting" with it, sandblasting your glass surface, or tack fusing some clear powder onto the glass, to create a rough surface for the chalk to grab onto, if you want to draw on the surface.
Glassline suggests that the piece be fired to 1500 degrees Fahrenheit, but they can be fired higher or lower depending on the desired results.