In Logatec, southeast of Slovenia’s capital, I have collected 4 different clays. Only one stands high temperatures, but it has one mayor fault. It contains very small particles of charcoal-like material. And because clay itself is very plastic and consists of finest of clay particles it is also a very closed clay body. The organic materials that then burn during the firing cannot escape from the body resulting in a bubbly surface. And the clay colour is a little boring too. That is why I tried to find a solution for this problem. Fixing closed clay bodies can be done with larger size particles like grog or sand. I chose Slovenian silica sand, which contains a little iron. I also wanted to create some depth, so I tried to mix in dried purple clay from Logatec and leftovers of light purple clay. I did 5 tests and only one was good enough at high temperatures, all the others melted:
This one I am happy with: iron from silica sand gave pale buff colour clay a nice yellow makeover and dry purple clay melted into dark green spots.