Beware of yellow pumice! It can be the result of high levels of boron, which may be phytotoxic. T > In Washington state, Verkist orchid nursery outside Bellingham sells (or used > to sell) both washed and unwashed pumice, the former in your choice of sizes. > It's been many years since I was there, but the price was quite reasonable. The > pumice they sold was a warm ocher yellow, very attractive.