glass casting

New Mexico Clay s tutorial on glass casting in a clay mold. Fire the clay mold 100 degrees hotter than you plan to use it. I fired the bottle glass to 1600 degrees 500 degrees, hour. So it took roughly 3 hours to reach that temperature. Then I held it at that temperature for 30 minutes. Next, I fired down as quickly as possible to 960 degrees, and annealed for 3 hours. The reason you anneal is because the glass is not uniform yet. Some areas may be hot, some may be cool. Annealing time will depend on the thickness of the glass.