Stone Mountain Clay & Glaze Co.

4744F North Royal Atlanta Drive
Tucker, GA  30084
PHONE (770) 986-9011 / FAX (404) 492-7190
Yes, we are open to the public! 

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Q: How can I prevent bloating/blistering with the black stonewares? When fired properly, both SMC black stonewares will give you a beautiful jet black canvas for your work-whether glazed or unglazed. Almost always, if blisters/bloats appear after the glaze firing, it is due to over or under-firing. Lighter clays are typically more forgiving of a wider-range of firing profiles, but the black stonewares are very gassy and need a proper firing-especially during the bisque. Let's break it down:
Bisque:  Cone 04. We cannot stress this enough. Cone 05, 06 are too cool for the black stonewares. Typically bloats, even if they appear after the glaze firing, are caused during the bisque firing. They may appear fine after the firing, but problems will often arise during the glaze firing if the pieces are under-bisqued. If you have a digital kiln, program it using the "slow bisque" setting to cone 04. Again, we can't stress it enough-SLOW BISQUE, CONE 04. The black stonewares do not need to be fired in a special format or on their own. Some clays will let you get away with a cooler or quicker bisque-the black stonewares do not. They require that you fire them properly, and all of our clays will work beautifully when fired the same way, in the same kiln load, as the black clays. We also do not recommend nesting pieces created from the black stonewares. If you have a sitter/timer kiln, follow the firing profile on our firing chart, taking note of the recommendations for the black stonewares.
Glaze: Cone 6. NO HOLD. Holds add heat. A 15-minute hold can send the pots in a cone 6 kiln to cone 7, which is too hot for many commercial stoneware glazes. Some clays can handle it, the black clays CANNOT. If you have a digital kiln, use the "slow glaze" setting to cone 6. If you have a sitter/timer kiln, follow the profile on our firing chart. If you are firing closer to a 7, please let us know-we can recommend clays and glazes in our line that will work well for you.

Attention Skutt Kiln users: If you have a newer model Skutt, that does NOT feature the Bartlett V6-CF controller, you may experience some bloating with Black Raven and other dark or speckled stonewares when using the slow program. Their newer kilns feature a controller that does not let you select between a bisque and a glaze profile, and therefor does not fire quite the same as other computerized kilns.  This may not impact your firing with lighter-colored bodies, but it often does with darker bodies. Their slow profile for cone 6 unfortunately fires almost twice as long as other controllers.

If you have this newer controller, we recommend that you continue to use the slow cone 04 profile for bisque in your Skutt, and test firing with the MEDIUM cone 6 program for glaze. This has proved very successful for many of our customers. The other option is to download and use the slow bisque and slow glaze firing profiles from the Bartlett website here:

With a typical slow firing, your bisque should last approximately 10-12 hours, and glaze firing should last approximately 7-9 hours. If you are experiencing odd firing results or noting times that are drastically different from these recommendations - please call us so that we can help figure out what's happening with your firing, and ensure the best possible results.

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