Sharpening Part 18 – The Nagura Stone

In the previous post we listed some of the tools and accouterments necessary for sharpening Japanese tools using waterstones. In this post we will examine one especially useful stone mentioned previously: the Nagura. I know, it sounds like the name of some smelly, creepy thing that crawled out of a mountain cave in Angmar in LOTR, but if you don’t have this Nagura, you should get one.

The Nagura Stone

Nagura stones have been used in Japan for millennia, but they are not unique to Japan. For instance, the Coticule stones of Northern European have been used with nagura-equivalent stones since before Roman times. And I would not be surprised if the same tradition existed elsewhere too, they are so useful.

A Tsushima Black Nagura stone 55x55x55mm

There are several varieties of Nagura stones mined in Japan, the two most popular being the grey/black Tsushima stone pictured above and the softer white Mikawa stone pictured below. I use a soft white Mikawa Nagura stone for my straight razor.

Mikawa Nagura Stone

The black Tsushima variety is cut from sedimentary stone on the ocean floor near Tsushima in Nagasaki Prefecture, located midway between Japan’s Kyushu island and South Korea. I believe it to be the best for general usage so I will discuss this stone in particular.

Like all Japanese natural stones, Tsushima Black Nagura Stones are sedimentary deposits created by airborne volcanic ash being sifted by distance and wind and filtered by waves and tides by the time they reach the ocean floor. But they have not been subjected to the metamorphic weight and heat that makes harder sedimentary stones, and are relatively soft and permeable. They also tend to crack in the same plane they were laid down to in, especially if subjected to wet/dry and/ or freeze/ thaw cycles, so special measures are necessary to protect them.

The Job of the Nagura Stone

The Nagura stone is typically used to perform five tasks.

1. Cleaning Finishing Stones: Finishing stones become contaminated with pixie dust and grit from rougher stones. A 10,000 grit stone with 1,000 grit particles mixed in is much less than 10,000 grit effective. If you think a stone is contaminated, wash it well with a scrub brush and clean water then work the surface with the Nagura stone to loosen and float up the contaminate particles, then wash off the slurry. The stone will be clean.

2. Removing Clogging: Similar to 1 above, the Nagura stone is effective at unclogging dried slurry and metal swarth from the sharpening stone’s surface helping it get back to work sooner.

3. Truing Stone Surfaces: Finishing Stones need to be trued occasionally, usually the corners and edges. Use the Nagura periodically to knock these high spots down. The resulting slurry can be used for your normal sharpening process without it all going to waste.

4. Reducing Startup Time: Time is money. Waterstones abrade most efficiently when they have a slurry worked up, but it can take time to get decent slurry started on some stones, especially hard ones, and with some blades, especially those with soft jigane. Use the Nagura to quickly develop this necessary slurry saving time and money. If you focus on the corners of the stones, which tend to be high anyway, it will contribute to truing the stone as mentioned in 2 above.

5. Reducing the Average Particle Size in the Slurry: Nagura grit is quite fine. You can add Nagura slurry to a stone (by rubbing the stone to create slurry at corners and edges, BTW) to reduce the average grit size of the slurry making a stone create finer scratches and a better polish. For instance, adding Nagura slurry to a 8,000 grit stone makes it polish more like a 9,000-10,000 grit natural stone.

Using the Nagura Stone

Nagura stones are just as useful when sharpening with synthetic sharpening stones as they are with natural stones. In fact, they may be even more useful with synthetic stones since synthetic stone slurry containing nagura particles more closely approximates the positive aspects of natural stones.

Nagura stones are easy to use. Simply wet the large stone and rub the small stone on its surface. You may need to add additional drops of clean water while doing this. The goal is to wear down the high spots on the large stone while at the same time producing a slurry mixture from both stones to use when sharpening blades.

The key is to pay attention, use your handy dandy stainless steel ruler to identify the high spots, and use the nagura on those areas first. Don’t be a ninny and rub the nagura all over the place willy nilly. Make a plan. Work the plan. Develop good habits and speed will follow.

If the large stone is already perfectly flat, and you need to produce a starting slurry, work the ends and corners of the large stone with the nagura in anticipation of those areas becoming high in the near future. That’s a good boy.

Protecting the Tsushima Nagura Stone

Nagura stones are fragile. To avoid water penetration and cracking, it is wise to use the side of the stone that was in a horizontal plane when it was formed. It is also wisdom to use only one surface of the stone and to coat the stone’s other 5 sides with paint to prevent water infiltration and cracking, and to keep skin oils from penetrating. Traditionally, natural urushi lacquer made from a poisonous tree sap has been in Japan used for this purpose, but any high-solids urethane will do the job.

The Nagura stone is a subtle tool. As your skill using natural sharpening stones improves the value of this tool will become apparent.

In the next article in this depraved series of sex and scandal we will discuss ways to maintain sharpening stones. Some people will be miffed. Others will be thrilled. What about you?

YMHOS

Links to Other Posts in the “Sharpening” Series

Sharpening Japanese Woodworking Tools Part 1

Sharpening Part 2 – The Journey

Sharpening Part 3 – Philosophy

Sharpening Part 4 – ‘Nando and the Sword Sharpener

Sharpening Part 5 – The Sharp Edge

Sharpening Part 6 – The Mystery of Steel

Sharpening Part 7 – The Alchemy of Hard Steel 鋼

Sharpening Part 8 – Soft Iron 地金

Sharpening Part 9 – Hard Steel & Soft Iron 鍛接

Sharpening Part 10 – The Ura 浦

Sharpening Part 11 – Supernatural Bevel Angles

Sharpening Part 12 – Skewampus Blades, Curved Cutting Edges, and Monkeyshines

Sharpening Part 13 – Nitty Gritty

Sharpening Part 14 – Natural Sharpening Stones

Sharpening Part 15 – The Most Important Stone

Sharpening Part 16 – Pixie Dust

Sharpening Part 17 – Gear

Sharpening Part 18 – The Nagura Stone

Sharpening Part 19 – Maintaining Sharpening Stones

Sharpening Part 20 – Flattening and Polishing the Ura

Sharpening Part 21 – The Bulging Bevel

Sharpening Part 22 – The Double-bevel Blues

Sharpening Part 23 – Stance & Grip

Sharpening Part 24 – Sharpening Direction

Sharpening Part 25 – Short Strokes

Sharpening Part 26 – The Taming of the Skew

Sharpening Part 27 – The Entire Face

Sharpening Part 28 – The Minuscule Burr

Sharpening Part 29 – An Example

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22 thoughts on “Sharpening Part 18 – The Nagura Stone

  1. Again, a really informative post Stan!! I have a few Nagura but all of them in the “white” colour…. Maybe I need to get one of the black one like you suggest!! I will look into it!
    Thank you
    It is officially the new year in your neck of the wood!! Have the greatest of year for 2020!!

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  2. I’ve never been a big fan of traditional nagura stones for jnats. I prefer the small Atoma 400 grit diamond plate on the (blue) plastic base for this purpose. I feel it has several advantages over a traditional nagura. I creates a slurry faster, the slurry consists only of stone material and it roughens up the surface of the stone more than a nagura which adds even more speed. I think you might like it if you give it a try.

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  3. Thanks, Henk. I have tried it, and prefer the nagura. I don’t want a rougher surface on my sharpening stones, effectively reducing the degree of polish it can accomplish until it becomes smooth again. I don’t want to wear out expensive diamond plates to abrade stone instead of the steel I need them to abrade.

    Liked by 1 person

    1. So I assume you use the 3 stones technique to keep your stones flat!?!
      What do you do with the expensive natural stones, having 3 of each seems expensive?

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  4. No, just 2 stones each of the 1,000 and 2,000 grit (and carborundum stone sometimes).

    I use the Nagura, and very occasionally (once a year?) the glass plate to true my finishing stones.

    Henk, if I may be so bold as speak for him (we have argued about this by email several times), prefers to use a diamond plate to true all his stones because it is quick and does a good job. He is right, except perhaps about the good job part, which is where we disagree.

    I think diamond plates are too expensive to use on sharpening stones because sharpening stone grit, while softer and less abrasive than diamond dust, is a lot harder than steel and wears the diamond plates out prematurely. I don’t consider that cost-effective. On the other hand, Henk uses his tools professionally, and time is money, so the greater speed of diamond plates may justify wearing them out sooner.

    Diamond plates also dig striations in the stone’s surface that make the stone of effectively rougher grit until the stone’s surface wears smooth again. The same exact thing is true when using a rougher stone to smooth a finer stone. How much rougher? It varies, but the difference in polish is clearly visible, and the time that must be spent on the next stone in the series is correspondingly longer, in my experience. This is why I prefer to use the same grit stone to true each stone.

    By using the same grit stone, I can true a stone while I am using it, without having to worry about grit (or diamond particle) contamination, which I have experienced with diamond plates but which Henk says doesn’t happen anymore. He may be right, I don’t know.

    As I mentioned in the post, by having 2 each of my most abrasive and hardworking stones close at hand, I start the workday with 4 flat, true sharpening surfaces, and don’t need to worry about flattening them until all four are dished. In my little workshop, I just work on one side of each stone, but when 2 stones become hollowed out, then I rub them together to true them. It is quick and easy and economical and the stones don’t contaminate each other.

    This is the traditional way. Is it the quickest? No. Is it the cheapest? Yes. Is it the best? Idunno. Maybe. It works pretty good.

    Stan

    Liked by 1 person

    1. Makes a lot of sense, to ma anyway!! I’m like Henk, I use Atoma diamond plate to flatten my stones…. I thought you needed 3 stone to make sure you end up with totally flat stones!! I’m considering going to the stone to stone method… I need to get more stones hahaha. I never use diamond plate for anything else than flattening my water stone…. And they don’t last that long and are not always as flat as people think they are!! So I’m sure a stone to stone system is more efficient in the long run!
      Sorry Henk I’m going with Stan!!

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  5. The only way to get stones perfectly flat is to use superflat ceramic lapping plates and fine powders. You can’t do it with a diamond plate or another stone.

    The float-glass plate I recommend is the closest economical method I know. Indeed, it tends to make stones convex in two axis, which is not a bad thing within limits.

    But a perfectly flat stone is expensive to maintain and not especially better for general woodworking than a pretty-flat stone. The rabbit-hole is not only deep, but sleepless nights and gibbering insanity await those who reach the bottom. Beware!

    Liked by 1 person

    1. Rabbit hole indeed!! I have a friend that compete in the shaving things you know the one at Kez…. Well it is an obsession and one that I almost got caught into, but I use my tools for a living and I can’t just fall in that kind of “craziness” hahaha.

      I’m pretty happy with my sharpening, especially in the last few months! But still lots to learn especially when it comes to finish surface, I hate to sand, so kanna finish is what I’m after and I’m there most of the time on smaller surfaces in easier wood…. But larger surface and trickier wood I’m still inconsistent.

      I really like the conversation here, You and Henk disagree with respect!!

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      1. So you know that rabbit hole then.

        Large surfaces with grain all over the place are difficult even for the very best. I could once hold my own, but that was many years ago when I used a plane everyday. You really have to stay on top of the dai.

        Sharp will only get you so far. Work on the dai and blade combination.

        Henk is a good man. I have not met him or seen his work in person, but he has shown me pictures. He knows what he is doing, and got excellent instruction from Japanese craftsmen back when. Everyone’s approach to tools and woodworking will be a little different.

        Liked by 2 people

  6. I used to get at least 4-5 years of service out of an Atoma 400 used only to flatten stones (everything from a Sigma ceramic 1000 to a jnat or coticule). I’m happy with that. I switched to a Kensyou 400 last year and I expect it will be just as durable since it’s made by Tsuboman. In between flattening I use the small Atoma as a nagura which is still large enough to keep even bench size stones flat quite a long time and it doesn’t cost a lot.

    Is it the best method? I don’t know but it’s quick and easy, I get the results I want and I need just two 400 grit diamond plates (the full size Kensyou and small Atoma) for all my stones. As for contamination by diamond particles, that has literally never happened to me.

    Liked by 2 people

    1. Still the method I use, and I think I will be using at least until my atoms 400 is dead. Maybe I should look into a Kensyou… There is also the nano sharp flattening plate that I heard only great things about… But pricey!!
      Time will tell!!

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  7. Stan, there was no option to reply to your last post/reply, so here it is! Indeed the dai tuning/conditioning is critical and man does it make a difference!! Still not the best at it and maybe a bit shy sometime scared to wear them out and have to cut an other dai(something I’ve done only once so far!).

    On an other topic, bevel angle, all the plane blades seems to come in at 25 degrees… I find that angle to be almost useless… So I regrind them(after using them a bit to see if I can work with it) to 28-30 degrees and seems to have a lot more success with that… But that is a lot of work and sometime lots of taping…. I wonder why the smith do it that way and not make it right away to 27-28* where from what I read seems to be where most carpenter/woodworker like to have there tools at?

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  8. David:

    Yes, new planes delivered with too shallow a bevel angle is a problem even for me. Blacksmiths are focused on making the blade and getting it out the door to the dai maker. Sadly, small details like bevel angle sometimes get overlooked. Professional sharpeners will do the same thing if you let them. But all I can do is scold them and ask them to do better next time.

    Please don’t grind your plane blade. It deserves better treatment than that.

    This is one of the few situations where using a honing jig like the Lie-Nielson widget or cheaper Eclipse knock-off makes perfect sense. With the blade locked into a jig at the right angle you can put it on your stones at the correct bevel angle to make a small secondary bevel (something I vehemently oppose in most any other circumstance).

    By using the sharpening jig at the same angle for a few more sharpening sessions, the bevel will gradually get wider a little at a time without wasting expensive steel or creating an evil rounded bevel. You will need to use the jig for a while, but eventually enough of the flat bevel will be established so you can stop using the jig and get back to freehand sharpening as the good Lord intended.

    Don’t let using a jig become a habit for normal sharpening, though. It’s very embarrassing. That would be like using a wheelchair to keep your shoes from wearing out: your shoes will look great but eventually you won’t be able to get around without it. Sooo embarrassing.

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    1. I already do this… not to that extend or should I say I use to do that before being comfortable with the low speed grinder…. maybe I go back that way… I hate the grinder but it is so quick and so far I never ruined a blade..

      Regarding sharpening jigs, what about the Japanese models? Or the sharp skate one?

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      1. I guess I’ll reply to my own post cause there is no option to reply to yours… I have the Veritas MKII and it is a good guide, but not so good with J tools because of the shape of the blades… As for Sharp skate, I can get one for a good price since Harellson Stanley offered me a deal a while back, maybe I will take him on it!!
        I have an original eclipse made in England but have a hard time to make it work properly!

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      2. The richard kell always intrigued me, so simple!! I just pull the plug on a sharp skate and we’ll see how it does!! Yesterday I change the bevel angle on my Yamamoto Guren 58mm and I used the Veritas MKII It went well, but it took some time on my 400grit water stone(hibiki I think, light green) anyway it is now at around 28 degrees I believe, and should last better! I have an other one to do today, a 70mm that will be a bit longer I guess!!
        Thank you again for the great communication and exchange! You hold a great blog, long life!

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  9. The low bevel angel on blades from the factory or blacksmith is something that bugs me as well. It’s easy to make the bevel angle lower with a minimum loss of material when the supplied bevel is 30 degrees or more. You will always lose too much steel, especially with a short oirenomi blade, the other way around.

    And here’s a little tip for dai tuning. Buy a cheap Stanley chisel, cut off the entire bevel and grind the end of the blade at 90 degrees. This makes an excellent push scraper that gives you lots of control over how much you remove.

    @ Davind Gendron: If you feel like making a new dai some day you might want to consider a Lignum Vitea sole. It doesn’t have to be thick, 8-10mm is enough. Just be sure to clean the side you glue to the block of white oak with acetone. Lignum Vitae is stable, hard, dense and very wear resistant but the best part is it contains a lot of oil so it’s self lubricating. No other plane sole glides across wood like Lignum Vitae.

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    1. I’m with Henk and David. Diamond stones to flatten. But that is just what I was taught. Although, it’s probably fair to say that it is now ‘conventional’ wisdom. Having said that, I would like to try the two stone nagura approach.

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