Sharpening Part 14 – Natural Sharpening Stones

The finest, softest natural stone your humble servant routinely uses. Black Cashew natural urethane paint (made from cashew nuts) has been applied to the bottom and sides to retard water infiltration and prevent de-lamination in this sedimentary stone. It is a joy to use, and all my blades simply wiggle with joy when its their turn for a ride.

Advice is a dangerous gift, even from the wise to the wise, and all courses may run ill.

J.R.R. Tolkien

We receive a lot of inquiries about natural finishing stones, so your humble servant wanted to share some accumulated thoughts and experiences about them with Beloved Customer. Perhaps they will be useful.

To begin with, natural Japanese stones are a lot of fun, and can create a beautiful, cloudy finish on a blade’s bevel. They truly make my heart sing, wild thing.

I believe that blades finished with a natural stone tend to stay sharper a little longer compared to synthetic stones, but can’t prove it. Despite my fondness for them, I want to make it clear that natural stones are not magic, and are not critical to doing good work.

It is interesting to note, however, that while top-quality natural stones are expensive, if judged by the amount of steel they can sharpen, they are actually no more costly than the better synthetic stones. But they can be more of a gamble.

Geologists believe (they weren’t around at the time to witness the event, although they like to pretend they were) that natural sharpening stones typical to Japan were created when particles of volcanic dust fell from the sky, were sorted, and sifted by winds and waves, and settled onto the sea floor eventually becoming sedimentary stone. Sounds likely.

Being natural, they carry the inherent and potentially expensive risk of internal defects, such as weakness between sedimentation layers, cracks, and contamination such as hard particles of sand concealed inside. Even if you find one that seems perfect in every way, the bones never stop rolling because you never know what lurks inside.

This stone is a medium hardness natural finishing stone I regularly use.
The stone is epoxied to a base made of Ipe wood. The sides are coated with a natural urethane called Cashew, a product of the cashew nut tree, to prevent water from soaking into the stone’s sides potentially causing cracks and delamination. The bright orange color is to ensure pesky pixies do not talk the stone into sprouting legs and walking away when outside the workshop. They can be persuasive when talking to stones, donchano.

Your foolish servant erred with his first purchase of a natural stone, one recommended by a hardware store owner in Sendai many years ago. I fear he intentionally foisted a low-quality stone on me that a person more experienced with natural sharpening stones would have rejected. This stone “drags” steel, a phenomenon where the stone deposits hard clumps on the blade that then gouge the stone’s surface and leaves rough spots on the blade. It’s impossible, BTW, to judge a stone’s propensity for this pixieish behavior by eyeball alone.

I learned a bitter and expensive lesson about both natural stones and salesmen that day. I still use that stone for sharpening axes and gardening tools and as a door prop, but the real reason I keep it around is as a reminder of my foolishness.

After that disastrous adventure, I became more careful and paid less attention to what people said or wrote. Consequently, I don’t give a rodent’s ruddy fundament about most people’s opinions on the subject of sharpening stones. Nearly all who claim expertise talk and write about things they only partially understand. Many have a conflict of interest. Still others seek justification of their poor decisions.

Nor I do care about the region or mountain or mine a stone came from, or its designation or color. A word to the wise a stone seller near Kyoto whispered into my shell-like ear some years ago: Even the best mines produce mostly waste.

And because of the impossibility of evaluating stones long-distance, and considering Gildor’s wise words quoted above, I am hesitant to give advice about what stones to buy or where to buy them. But I will tell you what I do when buying a stone:

  1. I examine the stone for cracks and signs of irregularities and impending separation at its sides (not all defects are fatal);
  2. I flip it with my fingertips and listen to the sound it makes. Yes, a good stone sounds different from a bad stone;
  3. I take the stone in my hand, close my eyes, and feel it with my ki 気. Does it feel sound and happy?;
  4. I touch my fingertip to my tongue, wet the stone just a bit, and smell it. Does the moisture soak into the stone quickly, or is the stone too dense? Is the smell clean or muddy?
  5. I touch it to my teeth (an ancient technique for detecting the fineness and consistency of a stone’s abrasive qualities);
  6. I put a plane blade I know well to the stone, take a few strokes, and like a bow on violin strings, I feel the friction and listen to the music made;
  7. I examine the scratches the stone leaves on the blade’s jigane and hagane using a loupe. 

None of these critical tests can be conducted long-distance. BTW, if you think any of them are pointless, then I know where you can get a good deal on some swamp land in North Korea with its own lake perfect for a condo development. Well, actually its a settlement pond for a chrome plating factory, but the effluent discharge was recently brought up to 1876 standards so there is no pesky vegetation, or endangered fish or wildlife to deal with, and the price is right!

I have two natural stones I use regularly nowadays. One is of medium hardness suitable for most every straight blade. The other, pictured below, is very soft, and easily damaged, but creates a beautiful foggy finish on the steel. 

I love my natural finishing stones, the feel of using them, their smell, the music they make and the pretty finish they produce on my blades. They are part of the romance unique to Japanese blades. I believe the stones I use now and their sisters worn to slivers in past decades were worth every penny I paid for them, but I recognize this is an emotional rather than practical viewpoint, and difficult to defend economically.

Don’t misunderstand: your humble servant is not suggesting you should not try natural sharpening stones, only that you carefully evaluate them in-person beforehand, and buy from a reputable dealer that offers a reliable warranty (please don’t ask for recommendations). And just to prove I am neither troll nor curmudgeon, I will give you the same advice about purchasing natural sharpening stones that a wise old man shared with me a long time ago, advice that has passed Gildor’s test.

  • Rule 1: Don’t trust your eyes alone when judging a stone’s origin, designation, appearance, or performance (see the five tests listed above): always try a blade on the stone before purchasing it to make sure it works for you and your blade;
  • Rule 2: Don’t buy a stone from someone you don’t trust and who won’t give you a reliable 30 day warranty to provide time to check the stone carefully for suitability and defects. Remember, the combination of stone and blade is much like a marriage where the softer (but actually granularly harder) stone smooths and polishes the harder blade. If the two don’t work well together, then even lawyers can’t make it right, but a warranty may help reduce the damage;
  • Rule 3: Don’t whine if the stone disappoints: roll the dice and smile at the spots they show you. Besides, hoes, axes, and hedge shears need sharpening love too.

On the other hand, if you have the stomach for Rule 3 and don’t mind risking your money, then the first two Rules can perhaps be ignored. I grew up in Sin City and know that can be fun too. You pays your money and you takes your chances; Baby needs a new pair of shoes!

Finally, if and when you find the perfect natural sharpening stone, I advise you to protect that lovely thing from damage to ensure it serves you long and reliably. The link below is to an article on this very subject: Protecting Natural Sharpening Stones


Ancient Roman or Norse dice in a pose worthy of gambling.

If you have questions or would like to learn more about our tools, please click the “Pricelist” link here or at the top of the page and use the “Contact Us” form located immediately below.

Please share your insights and comments with everyone in the form located further below labeled “Leave a Reply.” We aren’t evil Google, fascist facebook, or thuggish Twitter and so won’t sell, share, or profitably “misplace” your information. If I lie may I always roll snake eyes.

6 thoughts on “Sharpening Part 14 – Natural Sharpening Stones

  1. Beautiful stones, Stan.

    The fact that a natural stone’s composition inherently produces varying particle size may have something to do with the longevity of the edge.

    I love mine, their feel, the smell of the slurry, and the beautiful finish they produce…


    1. I agree with your take on the pleasant feel, smell, and appearance of natural stones. Synthetic stones just can’t match it. One reason the edge may last longer is that the grit particles of natural stones are rounder than synthetic stones so the scratches they cut into the steel are close to semicircular scoops in cross section whereas natural stones have sharp corners and cut scratches with a deeper “v” shaped cross section. These cross sections appear at the cutting edge. The theory is that the metal at the right and left of the deeper/narrower V scratches is weaker than those of the rounder scratches and are more easily damaged. The rounder/wider/shallower scratches of natural stones diffuse light in more directions than the more uniform V scratches of synthetic stones which explains why natural stones produce a misty appearance while synthetic stones create a mirror finish. Just what I have read.

      Liked by 2 people

  2. I love Natural Water Stones, their smell, the finish they leave on the tools, the fact that you need to learn to know there different characteristics(better in one area than an other) I dont have many, 3, but they are good, especially like the softer one, a bit easier in use!!
    I would love to get others, but since I don’t really travel and I don’t see myself going to Japan anytime soon, I will have to do with out more. I got burned a few times by my ignorance, on tools, stones etc and now I’m really careful of whom I listen too!!


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