INTRODUCTION & PRIMER

Below are more detailed 'Stone Sessions' that elaborate in greater detail the characteristics of each natural stone (tennen toishi), the sharpening experience on different steels, the results they yield, and what they may be best used for. It is important to note that since these are natural stones, it is very possible that every single stone, even quarried from the same strata at the same quarry, can be different from each other in their idiosyncratic characteristics; so it is very possible that if you have the some of the same stones as listed below, you may find that you have different experiences and results with them, which may be frustrating for some, but really speaks to how special natural stones can be; it is a relationship that takes time to develop a truer understanding with how your stone will interact with your steels. The details below should only be taken as a general reference of each type of stone. Stones are generally measured in mm as done below, but the density has been given in cm3 for a more digestible number. An initial slurry was not worked up before sharpening, as this adds an additional level of complexity to the sharpening experience that would would require additional explanation, which would become burdensome to include. This information is likely superfluous for some, but from an novel educational standpoint, it can be useful to gain an initial understanding to the mysterious world of natural stones; albeit, the best way to understand is to get your hands dirty.

In order to cover a broad spectrum of steels as succiently as possible, the steels listed below represent three widely common 'genres' of steel in the cutlery world - softer (~52-56 HRC) Western stainless steels (SS), and two of the most traditional Japanese steels, Shirogami, AKA, "white paper steel" and, Aogami, AKA, "blue paper steel" (both ~60-67+ HRC). Shirogami is a very pure steel, with essentially just high amounts of carbon (~0.8-1.35%), and iron, with as little trace alloys as possible, which allows it to take an extremely keen edge with the downside of it being relatively brittle. Aogami is a more complex steel with a huge amounts of carbon (~1.05-1.5%), as well as a number of alloys, such as tungsten, vanadium, and manganese, which gives it extended edge retention and resilience, with the downside of it not being able to achieve as keen as an edge relative to shirogami. There are different versions of both shirogami (1, 2, and sometimes 3) and aogami (super, 1, and 2), each with differing amounts of carbon, and alloys to give them subtly different properties, as well as different types of SSs that differ in both their alloy composition and quality. The versions used below are shirogami 2, and aogami 2, which are typically the most common forms of both and the SS is from K Sabatier, which in my opinion, is the best French 'Sabatier' brand (ie, a good quality SS). There are many different ways to test for hardness, but the most common in cutlery is the Rockwell Scale, specifically scale C, or HRC. A diamond tip is indented into the steel and the depth of penetration is measured to yield an HRC number; the higher the number, the harder the steel. Steels in cutlery typically range from 54-66+HRC, with some even reaching 69 or 70HRC. While hardness means a sharper edge can be acheived, it also means a more brittle edge, and care must be taken when using harder steels; softer steels can not take as keen an edge, but are tougher ie, they resist chipping and breaking, but loose sharpeness more quickly than harder steels. Pick your poison.

The characteristics listed for each stone, except the numerical measurements, are subjective. The more you get your hands on stones and see how other users have classified similar stones, the better picture you have to work with, and the easier it is to discuss such things with a good degree of confidence that you are on the same page. All grit numbers are in JIS ('Japanese Industrial Standard,' vs ANSI 'American National Standards Institute, the latter being what you find on sandpaper, etc, at the hardware store in the US) which is the standard for Japanese whetstones, and the specialty cutlery world in general. Given that these are natural stones ie, they do not come with exact measured grits like synthetic stones, it is best to give an estimated grit range, rather than assume an exact number. Natural stones can range from anywhere from a gnarly 300 - a wicked 30,000+. The lower the grit, the more metal will be removed in a shorter amount of time, and will also yield a 'toothier' edge, ie, an edge that has grip and tears through food like microscopic saw; while higher grits will yield keener/sharper edges that glides through food (or hair and wood).  Hardness levels are typically assigned 1-4, with half numbers in between, 1 being very soft, and 4 being very hard, some even add +, and ++ to further specify. Typically softer stones are beginner friendly since the stone absorbs any mistakes rather than the blade taking the impact on harder stones and possibly ruining the edge, and have greater tactile feedback, giving you a better sense of your angle and pressure. Softer stones also release their abrasive particles easier when in contact with the steel being sharpened, and create mud and swarf (togidoro), which can be utilized by the sharpener by maintaining or adding water levels to create different consistencies of muddyness to yield different results on the edge or surface of the blade. Harder stones do not give up their abrasive particles as easily, and yield very keen edges for knives with a very high hardness, or more typically, razors, chisels and planes where keenness is paramount. The hardness and density of stones usually depend on the strata they are mined from. Just like oil and liquid mixed, the denser water floats to the bottom, and you end up with two strata. Each stone, with its own grit and hardness, has its own place in a sharpening series, and work better on some steels than others, and are ideal finishers for some types of knife designs and tasks. Learning how all these factors (plus several not mentioned) intertwine to not only give a finished result, but a pleasant journey, is what is so endlessly entertaining and intriguing about whetstone sharpening.

Again, this is all for reference, please email me for more detailed explanations and related questions.

Atagoyama Awesado

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Chu Nagura

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Hakka Namazu Suita

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Hideriyama Asagi

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Kizuyama

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Mizukihara

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Narutaki Tomae

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Ohira Ao and Kuro Renge Shiro Suita

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Ohira Renge Suita

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Ohira-Uchigumori

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Okudo Momiji Suita

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Renge and Kuro Renge Maruoyama Suita

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Shoubudani Asagi Koppa

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Shoubudani Iromono Tomae

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Tsushima

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Wakasa Asagi Awesado

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Yaginoshima

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