I followed Kimura's basic approach and I'm really happy with the results, all things considered.
If you want a custom carved rock please message me. If the National show isn't canceled I'll likely be going so you can pick it up then or I can ship anywhere.
Excellent advice, I soak the rock thoroughly and yes it still gets all over my hair and eyes, even with protection, but thankfully it eliminates the fine particles. If you've never had a volcanic cornea scrub you're really missing out.
I'm not familiar with Tufa rock, I use essentially a giant piece of pumice to copy Kimura's technique. Perhaps there is a better rock available elsewhere; I've heard some people make them entirely from cement. Nothing wrong with experimenting. Always wear eye protection, harder rock can shatter and really hurt you.