Toishi

Whetstones, typically made of alumina, have been increasingly been used as a substitute for charcoal for the grinding and polishing steps involved in lacquerwork because of the consistent quality that can be found in the synthetic whetstones as well as the expense and difficulty of obtaining high-quality charcoal for the purpose. These whetstones are typical of the soft variety which wear away with use and can be easily shaped to fit into tight corners or to evenly polish curved surfaces. Literally: whetstone.