Whetstones are stones used in the Sharpening and HoningSharpening and Honing
Most cutting tools require sharpening. There are various methods and tools for sharpening. For very sharp tools like shavers, they often call it honing rather than sharpening. The most traditional method is to use [[Whetstones|whetstones]]. Whetstones have different grits or hardness/fineness levels and are used in progression from rough to smooth. You can also use files, leather strops, abrasive compounds embedded in cloth, wood or leather, the palm of your hand, cardboard, the bottom of a p... of knives, tools and razors.

There are synthetic whetstones created by compressing some abrasive material. There are also "natural" whetstones that are mined.

Whetstones are often sorted by "grit" which measures the abrasiveness of the stone. Sometimes people refer to the size of the particles in μ or other measures.

Natural stones do not have "grit" in the same way as synthetic stones because the particles in natural stones vary and when the particles come off of the stone creating "slurry," they also break down into finer less abrasive particles. The particles from Japanese natural stones are often described as "flakes." (Some argue that not all of them are flaky

Japanese natural stones are often rated with a "hardness" and a "fineness" where hardness is how easily particles are released and fineness more about the particle size. There is some controversy however, with some people arguing that Japanese natural stones all have diverse and roughly the same (2-3 μm size). Some people also talk about the "speed" which describes how quickly the stone works on the blade.

The general idea is stones have abrasives that take material off of the blade by gouging and cutting and leaving scratches. As you get to higher and higher grits, the particles get smaller and the amount of size of the scratches get smaller. At super high grits, you are moving metal around and not really removing much material from the blade.

The "finishing stones" at high grits are really mostly polishing.

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References:

• JNS Grit, Fines and Hardness - Japanese Natural Stones.com
• • TomoNagura.com - Run by Keith V Johnson who is a kind of grumpy guy but fairly knowledgeable. He has a lot of videos on YouTube and a store on Etsy.
• My WhetstonesMy Whetstones
  Japanese Natural Awasedo finishing stones. Left to right: Ohira Asagi, Ozuka Mizu Tomae, Nakayama Mizu, Shobudani Mizu Asagi, Ozuku Asagi Synthetic Stones Maker Grit Type Notes DMT 120 μm/120 mesh Dia-Flat Lapping Plate Atoma 140 Diamond Plate Naniwa 220 Flattening Stone Shapton 320 "Blue-Black" Kuromaku Naniwa 400 Super Ceramic "Spash and Go" Atoma 600 Diamond Plate Naniwa 600 Nagura Dressing Stone Yoshihiro 1000 Professional Grade Toishi Shapton 2000 "Green" Ku...

Where to buy

• SharpeningSupplies - Great general sharpening supplies store.
• Japan Stones - High quality Japanese natural stones site with great service, but small selection and fairly high end.
• Tomo Nagura on Etsy.