What is Uchigumori toishi in Japanese Katana terminology?

The Uchigumori stone (内曇砥石, Uchigumori toishi) is a type of fine-grained whetstone used in the polishing of Japanese swords. The powder used in the maintenance of these swords often contains powdered Uchigumori stone. In addition to the Uchigumori stone, there are other types of whetstones used in the polishing of Japanese swords, including the Kongou-do (金剛砥), Binsui-do (備水砥), Meikurado (名倉砥), and Narutaki-do (鳴滝砥).