Sharpening Part 14 – Natural Sharpening Stones

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

J.R.R. Tolkien
The finest, softest natural stone I routinely use. Black Cashew Urethane paint for protection.

We receive a lot of enquiries about natural finishing stones, so I wanted to share some of my thoughts and experiences about them with you. 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 make my heart sing, wild thing.

I think 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 do 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 that Japanese natural sharpening stones were created when particles of volcanic dust fell from the sky, transported, sorted, and sifted by winds and waves, and settled onto the sea floor eventually becoming sedimentary stone.

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.

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 separation. The bright orange color is to ensure pesky pixies do not talk the stone into sprouting legs and walking away when outside the workshop.

I erred with my first purchase of a natural stone. It was recommended by the hardware store owner in Sendai where I bought it many years ago, and 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 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 an expensive lesson about both natural stones and salesmen that day. I still use that stone for sharpening axes and gardening tools, but the real reason I keep it around is as a reminder of my foolishness.

After that first disastrous purchase, I became more careful and paid less attention to what people said or write. Instead I learned from people’s mistakes. And I considered motives. Consequently, I don’t give a rodent’s ruddy fundament about most people’s opinions. Too many 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. Even the best mine produces mostly waste.

And because of the impossibility of evaluating stones long-distance, and considering Gildor’s wise words quoted at the top of this post, I don’t give advice about stones, so please don’t ask. 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 take the stone in my hand, close my eyes, and feel it;
  3. I flip it with my fingertips and listen to the sound it makes;
  4. I touch it to my teeth (the surest way to detect the fineness and consistency of a stone’s abrasive qualities);
  5. I put a plane blade to the stone and take a few strokes, and like a bow on violin strings I feel the friction and listen to the music;
  6. I examine the scratches it 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.

I have two natural stones I use regularly nowadays. One is of medium hardness suitable for most every straight blade. The other (see the picture 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, the smell, 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.

And just to save you wasting your time with questions, allow me to explain that we don’t sell synthetic sharpening stones because we can’t sell enough to justify procuring enough volume make our prices competitive. Besides, shipping costs would be too high. And we don’t sell natural stones because we cannot provide a warranty on anything so unpredictable, and I really hate disappointing people.

Don’t misunderstand: I am 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 four points of sound advice about purchasing natural sharpening stones that a wise old man gave me a long time ago, advice that has passed Gildor’s test.

  • First, don’t trust your eyes alone when judging a stone’s origin, designation, appearance, or performance (see the five tests listed above);
  • Second, don’t buy a stone from someone you don’t trust and who won’t give you a reliable 30 day warranty. That gives you 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;
  • Third, always try a blade on the stone before purchasing it to make sure it works for you and your blade;
  • And fourth, don’t whine if the stone disappoints: roll the dice and smile at the faces they show you. Besides, hoes, axes, and hedge shears need sharpening love too.

On the other hand, if you can follow the last rule and don’t mind risking your money, then the previous 3 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. Viva Las Vegas!

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

YMHOS

© 2019 Stanley Covington All Rights Reserved

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5 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…

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    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.

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  2. It has been proven the minerals in a jnat interact with the hagane (don’t ask me what exactly happens) and actually harden it. I think it was actually Kinzaburo Usui who proved it if I remember correctly. That’s one of the reasons the edge lasts longer. Another reason is the irregular scratch pattern. The higher serrations dull first so instead of the entire edge dulling at the same time, like the way it happens with a synthetic stone, there’s a gradual dulling. As for stones themselves, I found after testing many, many stones, there’s very little difference between a super expensive and a cheaper stone. I also found a good stone likes pretty much every steel you put on it and any differences are mainly attributed to the jigane. How soft it is, how it feels on the stone, and how easy it pulls material from the stone.

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