That's a cool effect, Biglou13, but that's not what I'm looking for (although maybe I'd like to know more about that, as well). I can't find a picture of the cork effect in pottery, for the same reasons as I'm having trouble finding information - I just get results about using cork plugs in pottery, or cork items at Pottery Barn, or pottery from Cork in Ireland. I did have a couple of pieces with this effect at my Mom's house, but God only knows where they are now.
But the effect is like cork board. I've attached a picture of cork board, and the pottery surface I've seen is remarkably like it. I think sometimes an artist will sometimes add a wash that darkens the crevasses. I would contact the artists whose work I've seen, but one of them is long deceased, and the other I just saw somewhere long ago, and can't remember.
If anyone can recall who might have mentioned this previously, please let me know!