- Japan's geology provided stone types that were composed of fine silicate particles inside of clay matrices. These stones are softer than even Novaculite, which are flint or chert rocks found in Texas, Oklahoma and Arkansas. They are sedimentary rocks and generally found in an area just north of the historical city of Kyoto, called Narutaki.
- In sharpening stones there are some benefits to using soft Japanese rocks over harder varieties. Because these stones are softer and finer, they do not run the risk of becoming either loaded or glazed with the items that they are sharpening. Also, they can easily be lubricated by using water instead of oil. Also, since these rocks are very soft, the water and worn materials make up a slurry which can sharpen and polish the blade.
- There are also some negative factors to Japanese sharpening stones that could cause you to consider using harder variations of rocks. The main disadvantage to Japanese sharpening stones is that they wear out much faster than other harder types of rocks. However, this also makes them a lot easier to flatten and smooth out.
- There are considered to be three levels or grades of Japanese sharpening stones. The first grade is rough stone (aka arato), the second grade is medium/middle stone (nakato) and the third grade is finishing stone (shiageto). There is also a fourth variety of stone called nagura, however, this sharpening stone is not used directly. Instead, it is utilized in order to make a cutting slurry on the finishing stone.
- There are various online vendors that have extensive and diverse selections of tools (including actual Japanese sharpening stones themselves) to use with your Japanese sharpening stones. Some excellent places to check out include Sharpening Supplies, Amazon.com, Blade Gallery, The Japan Blade, Smith's Edge, McFeelys and many others.
