Tanaka Toishi Yaginoshima Natural Stone Type 40

Natural stones, or JNATS or Tennen Toishi are natural sharpening stones quarried in various mountains in Japan. Made by natural thanks to Japan’s rich sedimentary and geological history. Japan is one of the only countries where such a diverse amount of silica and aluminium oxide rich stone can be found. These two elements give the stones the ability to cut steel in an effective way. The presence of natural sharpening stones is what gave Japan its history of swords and high quality tools. They have incredible historic and cultural value and the world of naturals is as complicated as it is fascinating.

Tennen Toishi can produce result unmatched to any man-made sharpening stone. They last longer, make better edges and can produce amazing polishes.
Rated on size, hardness, fineness, evenness and cutting speed with large, fine, fast and clean stones often being the most desirable.
It is difficult to generalise but some mountains or mines are known to produce certain characteristics. With known origin and layer one can form suitable expectations but each stone should be tested individually.

Jnats are slash ‘n go stones and do not need soaking. Often you’ll see that the high quality stones are sealed with urushi lacquer, or even glued on a little wooden board or stand. This is to provide extra strength since natural stones can be fragile. Do not drop ‘m and seal or support them if not done already.
On this website natural stones are rated with a 1-5 score for hardness, fineness and cutting speed, 5 being hardest, finest and fastest. Weight and dimensions you will also find below.
Natural stones are divided into three groups: Aratoishi (coarse), Nakatoishi (medium) and Awasedo (fine). The rating applied is relative to the category of the stone. A 3/5 fineness Nakatoishi is not as fine as a 3/5 Awasedo.