oddartist Posted November 9, 2016 Report Share Posted November 9, 2016 I am a long-time clay buff, but am only beginning to truly explore the medium, especially the chemistry end. I was never good in Science or Math. So - I have some local clay I'm trying to learn more about. I made a little cone of it and put it in a tray with 07, 05, and 04 cones and bisqued it. The 07 cone had fully melted but the 05 was still standing. The clay however, crumbled back to a slightly darker version of what I started with. Does this mean I need to fire it higher, or is it indicative of the raw clay needing something to improve it? I know it's all about exploring but it would be nice to know which direction to look. My guess is to make more cones and trays and keep turning up the heat, but I'd hate to waste my small stash just testing. With proper rainfall, my dig will be hundreds of feet underwater. :-) Point me the right direction? Link to comment Share on other sites More sharing options...
curt Posted November 9, 2016 Report Share Posted November 9, 2016 Have a look at this link http://community.ceramicartsdaily.org/topic/14935-native-clay-odd-smell/?p=111579 Link to comment Share on other sites More sharing options...
glazenerd Posted November 9, 2016 Report Share Posted November 9, 2016 Light to dark indicates iron. Link to comment Share on other sites More sharing options...
glazenerd Posted November 9, 2016 Report Share Posted November 9, 2016 Odd: run this simple body: 50% native clay, 25% silica, and 25% nep sy. Mix a 1000 gram batch and make a couple of small cylinders and 2- 1" x 5" test bars. Use one cylinder for testing a simple glaze, the other for weeping. The test bars fire unglazed and measure length to determine shrinkage. After you mix it, let it stand a few days before you wedge it to allow moisture to wet everything. After you wedge it, roll out 1/4 pound by hand into a 1/2" tube.Wrap the coil around your finger loosely: if it does not show any cracks your clay is very plastic, very small to small cracks medium plasticity; large cracks to tears equal no plasticity. You can cure any plasticity issues with the addition of ball clays such as FHC or OH #5. If you have some sieves around: say 80-120 run some through dry: figure out your particle sizes. Nerd ...still does not mean it is good clay for pottery, but will give you some working knowledge. If it turned darker during bisq, odds are it is high iron. Link to comment Share on other sites More sharing options...
alabama Posted November 10, 2016 Report Share Posted November 10, 2016 1. Find out if your sample is truly clay or dirt with clay-like properties. 2. Will it make a coil, and can that coil make an overhand knot? Without breaking! 3. Its easier to find large veins of clay on the bluff side of a river where the stratified layers of topsoil, sand, gravel, and clay is visible. The bluffs around here where there are two stratified layers of clay, the lower clay source is better. 4. Keep testing! Alabama Link to comment Share on other sites More sharing options...
PeterH Posted November 10, 2016 Report Share Posted November 10, 2016 This might be of relevance. Sedimentation Test http://www.gaiacollege.ca/course_content/3-DaySoil/Day%202/Texture%20Test.pdf Regards, Peter Added: Remembering the rather squat jar in the illustration, I was going to add that I would use a slimmer one. Rereading the pdf, they say just that: A tall slender jar is best. Link to comment Share on other sites More sharing options...
oddartist Posted November 12, 2016 Author Report Share Posted November 12, 2016 Nerd- I did mix some of this about 50/50 with some B-mix I had laying around and threw a small bowl with it. It fired to cone 04 okay but turned the B-mix sort of pinkish. Never did try to glaze it or fire it hotter. Link to comment Share on other sites More sharing options...
glazenerd Posted November 12, 2016 Report Share Posted November 12, 2016 Odd: Pink at bisq indicates iron as well. Mixed 50/50 with B-mix and you still got pink: I would say fairly high iron. FHC, OH5 ball clays run between 1.4-1.8% iron content and do not discolor bodies: my educated guess is your native clay is well above 4% iron content. You have come this far, might as well fire that puppy up. Put it on an old shelf, put a heavy layer of cheap silica under it just in case it does weird things- like melt... Nerd Link to comment Share on other sites More sharing options...
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