This clay comes from an odd low spot, on top of a hill on our land. Right out of the ground, it’s very silty and not plastic enough to throw, fires to above cone 8. Remove the silt, and drying shrinkage is around 15% (just drying not drying + firing shrinkage). Almost impossible to dry without cracking but fires to cone 5 with 0.1% absorption.
Now here comes the fun stuff. Remove all the clay from the silt, and wash it well, and it makes a wonderful silica sub for glazes right out of the ground, a fine powder, 96% silica with 0.5% iron. I took a break of about 2 yrs for family reasons and when I got back, I couldn’t remember exactly how I had processed it for the silt. How much did I let it settle, and which settled layer did I use?
So, while processing it for silt, I moved too much of the silt into the clay I was saving. This was the result. Threw great, was nice and smooth, and dried without cracking even when not covered.
Almost cone 9 oxidation. Absorption is only 0.3%. This was with a 3 hr boil with a 21 hr soak for a total of 24 hrs in water. I should be GTG for cone 8-9 oxidation. I still need to test for fired warping and glaze fit and see how it holds up in reduction. So the next step is to make some mugs and see how well they hold up to with different tests. I’ll probably also do a cone 6 tests just to see what the absorption is. And…I never did test fired shrinkage, so wouldn’t hurt to do that as well.
This leaves me with a problems #1 I still need more silt for glazes and #2 I’m not sure how much of the silty layer I added back to the clay. Goes to get shovel….
