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Susan Herre

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  1. I see... Quartz Inversion After dehydration, the next change that happens during the firing process is Quartz Inversion, which happens at 573 degrees C (1064 degrees F). At this point, quartz crystals rearrange themselves into a slightly different order. A slight and temporary increase in volume occurs at this point. This is why you always need some space around pieces during firing, as they will expand somewhat. Firing should proceed slowly during this Quartz inversion. A large percentage of ware that is cracked during the clay firing process happens from fast firing through this stage. The factory set program on electronic kilns usually slow down the firing at this stage for you.
  2. Thanks for your comment. I understand that our group studio does this: Bisque fire (06) overnight for 12 hours. Because of the conversion chart attached, I assumed this is 1828 or 1855 F. Is the 563C that you mention Celsius? = 1045.4 Fahrenheit. Is there a range of temps considered "bisque firing?" Thx
  3. Please see the crack near the bottom of three sides of this piece. The crack occurred with bisque firing (I am in a group studio.) I think perhaps the walls were too thin. . .?? Can anyone suggest other reasons for the crack? The clays are Laguna (WC871 Calico and WC401 BMix-5) Cone 5. I would like to clear glaze the piece and fire it at Cone 5. Do you think the crack will break open / break the piece completely? Thank you for your input.
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