I had no idea you included potting (as opposed to pottering) in your many talents. I was a potter in a former life and, although I was taught by followers of Bernard Leach who rather pooh poohed American Raku, I always found it a lot of fun. One friend of mine who lived on a boat came up with the idea of soaking his raku vases in the same stuff he used to waterproof his boat, which eliminated the problem of water rings. Probably wouldn't work too well on mugs, though...