Looking to mix up a nice black clay body that will fire well at cone 10 with a 10-12% shrinkage.
Short story long..., been taking a class and my instructor has a nice black clay body he uses for slab work. It's the 'studio mix' (a blend of whatever cone 10 clays used ... Laguna's mainly I think, CA-2, Bmix, etc... that are recycled from classes, then he adds about 50% C red and Grog.).
I tried to throw it but he uses 30 mesh grog and quite a bit of it so it was just a brutal throwing. Really rough on the hands just to center.
So we discussed mixing clay and he set me off to mix up the same clay body, just with less grog and I used 60 mesh instead.
It throws great. I mixed 50 lbs and threw some really great stuff, really focused on throwing thin wall, nice forms , etc.. Really put a lot of work in. Glazed one piece and while it was in high fire started mixing another batch. (was using an rarley used white shino.. it was for a show). The other pieces I held off on due to timing...
So it comes out of the kiln, goes into the show and a few days later has massive cracking all around the piece. By now all my other work is glazed and being fired. (this is all now chipping and breaking - clay shrinking more than glaze?)
The instructor NOW mentions he adds about 10% Feldspar to his mix, that I should have done tests and it was an 'expiremental clay body'. I feel like he sabotaged me. Why would he fail to mention this critical element as he watched me work hard for a few weeks, then mention it as if it was noi big deal?
So I am down 2-3 weeks of work that was supposed to stock a gallery for the summer (busy season is hitting now and I am completely broke, living on scraps to try and make this work)..
I have completely lost faith in him and don't trust his advice at all so I am looking for help to develop a black stoneware that is balanced with 10-12% shrinkange rates.
At the studio I have access to the basics (Feldspar, frit, c red clay, iron oxide etc..) but in recipies online there are often 5+ components of very specific names.
Here is a pic of the first piece I lost, fresh out of the kiln before the cracking started . Had several interested parties straight out of the kiln so it was a real blow.
thanks_Terry Sheppard.jpg 273.38KB 1 downloads