WarmGlass.com

Help
I have slumped soda glass with success twice in 2 greenware molds that I recently purchased. On the 2nd firing one deveoped a hairline crack and on the 3rd firing the other developed a crack. The molds are not the same size and both were bisque fired to 1100C at 100C per hour.

thanks

Kerin

Kerin, a little more information would help us help you. What cone clay was your greenware made of? What was your slumping schedule, rate of rise, target temp, hold time for each segment? The rate of temperature rise is as important to know as the final temperature. With this information we might be able to offer suggestions.

Best wishes,
Tom in Texas

sounds like you are moving through quartz inversion range too fast for your molds. that is in the 550 - 650c range i think. 1150f or thereabouts. large flat ceramic pieces are prone to this. i sometimes stilt large molds or put down a little sand so they can move on the shelf and/or heat more evenly. rosanna