At Pinecroft we have used a lot of black walnut. It makes us suffer in many ways since it does want to coal up in the firebox but damn the surfaces are nice and juicy. There is some thing in those nuts that is providing a lot of alkaline vapour to give the pots a orange peel surface. Salt or soda has never been used in the kiln. The same clay is also much darker. This could also be because of Emma's lust for hard core reduction.
I like the natural salting caused by the vapour in the wood. One of the other qualities of the black walnut is the big bark which I maintain holds all the good stuff needed for a good surface.
So you thought the back up sensor was invented in America- hah! This Chinese farmer found if he backed into a fence he would hear a loud squeal. Hurray for nuts!