Just recently I started using this Cassius Basaltic Clay. And I love it. How dark it can get reminds me a lot of steel. But it is hard to find a glaze to work well with the clay. The clay has a lot of gasses that come off of it when fired. And it has to be fired in an oxidizing fire, usually in an electric kiln.
Here is a bowl with a jagged edge. I am surprised that the jagged lip survived through firing.