I have some local dug clay that I mixed up with some Lincoln fire clay and some prepared high fire stoneware clay then and ran it through my bisque firing at cone 06 electric, and it turned out pretty nice. I very nice orange color. It throws well and looks great like I had said. However when I ran a small piece through my cone 10 reduction gas kiln it slumped and fell into a blob. I testing to see if at cone 06 the piece would hold water, but it leaked pretty heavy so I know it is not vitrified.
Now my plan is to get an entire load of this stuff and fire it to cone 01-1 and see what happens. I suspect it may be closer to the right temp. however you cannot just buy a few cones you need to buy an entire box. What do you guys usually do? Bite the bullet and buy a bunch of cones, or just rely on a pyrometer for the test firing?
My other plan was to put a small piece right near the peep hole in the next firing then record when it slumps and then I will at least know what the limits of the heat would be.
What do you all do in cases like this?