Japanese Whetstones (Whet meaning sharpen a blade) are used to grind and hone the edges of steel tools and implements. Japanese stones are called waterstones because water is typically used to help lubricate them and assist in removing debris.
There are Four Grades of Japanese Sharpening Stones:
Ara-to (Rough Stone): Used when the blade is dull with chips or nicks. These stones are softer, and they do not become glazed or loaded with material. Stones from 120-400 grit.
Naka-to (Medium Stone): Typically used for most sharpening. Stones from 700-2000 grit.
Shiage-to (Finish Stone): Used to eliminate fine scratches left by coarser stones and remove the fine burr created during previous sharpening.
Nagura: Used for finish stones which are too dense to create their own slurry.
Due to the scarcity of natural stones, synthetic stones have risen in prominence and, in fact, are considered superior to natural stones due to their consistency. When considering which sharpening stones to purchase it is important to understand that each brand of stones has a different consistency. Blades, knives and implements are made from different steel with a range of hardness. A range of stones from different manufacturers may be needed to bring your tool to a razor’s edge.
A typical sharpening sequence is to first establish a flat bevel and remove any nicks with one of the very coarse or medium coarse stones. The choice of grit depends basically upon how much material needs to be removed from the bevel in order to leave a clean, true edge. If there are no nicks or other defects, the 1200-grit or perhaps the 2000-grit stone is the best choice. However, if more metal needs to be removed, the 700-, 800- or 1000-grit stones cut faster. This is of course means less effort will be required.
The 80 through 400 grit stones are the best choice when a considerable amount of metal must be removed. Keep in mind though; these stones will leave scratches which must be removed with a medium coarse stone prior to final polishing. After the medium coarse sharpening is completed and a “burr” is obtained, the tool is transferred to a finish stone and alternately honed on back and bevel sides until the “burr” is totally removed. Finishing or polishing can be accomplished in one step, with any stone from 3000 grit to 8000 grit. However, in general, a better edge will be obtained if the tool is first honed on a 3000-grit or 4000-grit stone prior to final polishing on 6000-, 7000- or 8000-, 12000-grit stone.