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Re: Sharpening stone

Author: Elmore
Date: 2007-11-24 23:23

Japanese waterstones

Two Japanese waterstonesThe Japanese have traditionally used sharpening stones which are lubricated with water to sharpen their metal tools. (Using oil on a waterstone is deleterious to the stone.) As they have been doing this for many hundreds of years, it is obvious that the first stones were those which were found occurring naturally. The geology of Japan provided a type of stone which consists of fine silicate particles in a clay matrix. This is somewhat softer than Novaculite.

Japanese stones are also sedimentary. The most famous are typically mined in the Narutaki District just north of Kyoto.

Advantages and disadvantages
These softer Japanese stones have a few advantages over harder stones. First, because they are softer they do not become glazed or loaded with the material they are sharpening. New particles are constantly exposed as you work with them and thus they continue to cut consistently. Second, they can be lubricated effectively with water (rather than oil, which can ruin the stone) so nothing but water is required. Finally, because they are soft, the worn material and the water form a slurry which in conjunction with the stone, sharpens and polishes the blade.

The disadvantage is that they wear out faster than other types of sharpening stone, although this makes them easier to flatten.

Grades of waterstones
Historically, there are three broad grades of Japanese sharpening stones: the ara-to, or "rough stone", the naka-to or "middle/medium stone" and the shiage-to or "finishing stone". There is a fourth type of stone, the nagura, which is not used directly. Rather, it is used to form a cutting slurry on the shiage-to, which is often too hard to create the necessary slurry. Converting these names to absolute grit size is difficult as the classes are broad and natural stones have no inherent "grit number". As an indication, ara-to is probably (using a non-Japanese system of grading grit size) 500 – 1000 grit. The naka-to is probably 3000 – 5000 grit and the shiage-to is likely 7000 – 10000 grit.

http://www.leevalley.com/wood/Search.aspx?c=1&action=a&ap=1#start

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