A prominent feature of my recent life has been wild ceramic-ing, with clay dug from our patch of land in the Oregon forest, and some pretty rustic pit-firing endeavours. Below is a summary of my process.
slake to mush
Cover the dry clay with water and leave for 24 hours. For some reason this prompts it to deshacerse and totally go to mush.
Nice tray of homogenous slip.
Once you’ve shaped it and COMPLETELY dried your pieces, dig a pit and fill the bottom with cedar kindling. Stack the pieces on top and build up wood all around. Set it on fire! It has to get over 1000 degrees Fahrenheit to become ceramic.
Dry it out completely.
Mix it to make a watery slip, and then you can pour it through a mesh to filter out any lumps of wood, roots, pine needles etc.
Dry it out a bit
Just until, when you prod it, it feels like a good consistency for shaping.
Dig out your stuff
The next day, when things have cooled, you can go back and dig your pieces out of the still-warm embers. Somehow I have only had one thing suffer so much as a chip.