I have received many requests recently from people looking for full sized Uchigomori stones for sword polishing.
I’ve come to realize that there is much misunderstanding about this type of stone!
(All info listed here comes from stone wholesalers, miners, and Japanese natural stone experts!!!)
Uchigomori is used as either full bench stones or finger stones to produce a traditional cloudy finish during sword polishing, specifically on Tamahagane blades. They are known for their super soft particles and binder that will not scratch Tamahagane steel. It is important to realize that Tamahagane is quite a soft steel and thus can’t take an extremely fine polish, so it get easily scratched when harder stones are used. Because of this, Uchigomori stones are usually between 3000 and 5000 grit, not more. So are not nearly as fine as many consumers and some vendors believe. Uchigomori are also very slow stones that are not suitable for sharpening, as many think. Instead, these relatively coarse soft stones are only used for one specific task during the polishing process; to bring out excellent contrast by producing clouds in Tamahagane or exacerbating the differences found in Hamon blades.
It is also VERY IMPORTANT to note that Uchigomori Stone only comes from 2 mines; the Ohira and Mizukihara mines. If you find a stone listed as Uchigomori from another mine besides the ones listed above…IT IS A FAKE. This is more common than you may realize because of the rarity and high price that good quality authentic Uchigomori fetches in Japan. These are tremendously sought after and highly prized by professional sword polishers in Japan because top quality Uchigomori stone will not scratch rare Tamahagane or cause an uneven finish. Professional sword polishers are also given their first choice of stone, which has 4 repercussions for everyone who is not a professional sword polisher living in Japan. Foremost, bad quality stones, those which have toxic lines and rust like inclusions, are the norm from many online vendors. Secondly, when a vendor does get good quality Uchigomori in stock, it is at an extremely high price, and is usually in finger stones, because most will not be able to afford bench stones. Lastly, because of the prized nature of Uchigomori, fakes are becoming more and more prevalent, even from seemingly honest vendors. Also, please note that 98% of authentic Uchigomori stones sold from the Ohira Mine are sold as rough stones, meaning they have chiseled surfaces on all sides (unless they are already used), so sword polishers can flatten and shape them to a particular size and use.
As an alternative, there are many stones you may want to consider. I would recommend starting your search for an alternative by considering a natural sharpening stone between Lv2-Lv3, but not more than Lv3. Currently, in my store I have several stones from the Ohira, Nakayama, Hakka, and Atagoyama mines that would work excellently for most customers needs. And if you are one of those that require good quality Uchigomori, please try finger stones instead of full sized bench stones because in the end, they are much more affordable, better quality, and easier to procure ;)
Real Uchigomori stones from Ohira Miner: