I have collected a huge range of clays from various places that just won't stand stoneware temperatures. Some of these will only take an earthenware firing and others can be nudged up to midfire temperatures as long as the firing isn't too long. I've been trying to decide what to make with these and how exactly to fire them and finally made a decision over the summer.
I used clays from Leicester, North Devon and a river clay from mid- Devon, often mixed with quartz or crushed rock from the area they came from or homemade grog (!) from the same clay, to try and control the high shrinkages. I fired to cone 9, which in my experience is the equivalent of around cone 7 in a non-wood firing. A previous firing to this temp gave a uniform leather brown on everything that came out of the kiln, so this time I decided to change the habit of a lifetime and do a reduced cool. The small kiln drops temp. pretty quickly once the firing is over, so as it dropped to 1000C in about 2 hours, I stoked small pieces of wood and bark in through the sidestoke port fairly regularly, to maintain a nice soft reduction flame throughout the stack and just a small amount of smoke seeping through cracks in the top of the kiln.
Apart from a collapse it was an excellent firing and I began to see what reduction cooling can actually do. There was some wonderful colour variation, black carbon trapping, haloing around wads but most impressively a gorgeous lustrousness to many of the clays. Definitely a starting point for more experimentation.
