merry Posted August 17 Report Share Posted August 17 I've been digging up clay and refining it. Should I just make several of the the same items and start firing at a lower temp then work my way up with each one to find the right firing temp? Quote Link to comment Share on other sites More sharing options...
Hulk Posted August 17 Report Share Posted August 17 Hi merry, welcome to the Forum! Good question, check back for input from raw/wild clay experts, and meanwhile, place your tests on broad/wide "cookies" of known clay to protect your shelves and kiln! ...for a completely unknown clay, a cookie with a "moat" to catch any liquification comes (almost) immediately to mind. Pres, Bill Kielb and Kelly in AK 3 Quote Link to comment Share on other sites More sharing options...
Bill Kielb Posted August 18 Report Share Posted August 18 I am with @Hulk but also want to point out that the geology in your area may or may not remain the same. So over time you might experience different firing ranges as the geologic composition may slightly change with the batch retrieved. Kelly in AK 1 Quote Link to comment Share on other sites More sharing options...
merry Posted August 18 Author Report Share Posted August 18 So far its all from the same batch. There is a 15 foot cliff in my river bed on my property it has an enormous layer of clay exposed. I'm not against just trial and error. It just for entertainments sake that I'm doing it. Hulk, Kelly in AK and Bill Kielb 3 Quote Link to comment Share on other sites More sharing options...
Kelly in AK Posted August 18 Report Share Posted August 18 The way I started this was, since I regularly fired clay at two temperatures (cone 04 bisque and cone 6 glaze), was to put samples in the ordinary firings. In a bowl of course! My clay was porous but dense and strong at 04 and definitely melting by cone 6. So I knew it matured between those two cones. I did what you describe, a few firings to dial it in. Cone 03 then cone 02 and I had an answer, 02 was too hot. A few firings was all it took to narrow it down to a cone range, but test tiles and pots are different. It took a few more firings to really dial it in and adjust for the way clay gets soft, pyroplastic, when it’s becoming vitreous. Then a few more to find glazes that played nice with the clay. I suggest you make tiles and small objects to start. If you make a flat bar of clay and support it on each end you can see how it might sag at a given temperature and that can be very helpful. Some clays will bloat and melt before they become vitreous, others will vitrify over a range of several cones. My local clay vitrifies within one cone before bad things start to happen. It’s a wonderful journey, a beautiful thing, digging this stuff up and making something worthwhile out of it. More of a long game I would say. I just started processing another hundred fifty pounds, just to be sure I’m good through winter. Wishing you luck and hope to hear how things unfold. Hulk, Min and Bill Kielb 3 Quote Link to comment Share on other sites More sharing options...
neilestrick Posted August 25 Report Share Posted August 25 Once you figure out the firing temp of your clay, you can modify it with other clays or feldspars to adjust the firing temp if you want it to be usable at a specific temp. You can also use other clays to modify the workability/plasticity of the clay. Quote Link to comment Share on other sites More sharing options...
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