Since glazes are still for now off-limits (though I did see a pot in a gallery that was glazed and just had traces of firewood stuck in the glaze–intriguing), I have been working with other effects. These are very unpredictable, which is a bad thing and a good thing! I have been working a lot with white clay just so that I can properly see the effects, because it’s really interesting. My land-dug clay is an entirely more interesting beast on its own: it looks grey when you first dig it, yellow when processed and you’re working it, and then it fires as a rich mix of blacks and reds. One of these days I am going to figure out why.
One effect to work with is simply oxidation. If you put pots in a fire, you can get some really interesting smoky effects, though you don’t get a lot of control.
One way to get more control is to wrap them up with organic matter that will smoke and mark the surface.
On one of these you could actually pick out the shape of the foliage it was wrapped up with. I think I’ve concluded that just a couple of small pieces of organic matter work best, so as to only ‘smoke’ portions of the pieces.
To promote more interesting effects, I also paint some of my pots with oxides. You can do this by mixing them with slip, as in the below examples (from top left: iron oxide slip painted on and design added sgraffito style, bands of iron oxide and copper carbonate slips, same pot fired, copper carbonate slip, cobalt oxide slip, band of iron oxide slip). I used 50:50 iron oxide to clay, and more like 1:20 for the copper carbonate and cobalt oxide since it sounds like they blacken very easily. The iron oxide gives a nice red; the others seem less predictable.
You can also just paint them on neat, which I did in rough brushstrokes on the below examples. Note: the top left pot showed some hints of green from the copper carbonate, which stayed after washing off the pot and I absolutely loved, and I was thrilled when the second one along which I did by the same method came out with these glorious green patches–but this time they washed off! Always unpredictable, I suppose. In my first (top-left) experiment, I put just a little organic material in with the pot, and got a really interesting mix of oxidations; in subsequent experiments, I suspect I put a little too much organic matter, which resulted in darker shades all around.
Finally, I recently started painting pots with a wash of copper sulphate–the kind used to kill slugs! This, for reasons I have yet to learn, creates some really interesting, crystalline, starry-looking effects. I noticed that the wash as it dries on the pots sometimes forms crystalline patterns; I also remember there being a few undissolved chunks left on one of the pots, and I wonder which of these created the effect.