Waterstone testing, the results. Part II.

Hello again faithful reader,

And checking the logs, there are a great big bunch of you now…

We left off last time with some pretty raw results, and they only showed how fast each stone got the job done. There are other factors to consider, each of which are important in their own way.

Typically, how quickly a sharpening stone works is a factor of what it’s made from and how it’s made. Traditionally, the fastest waterstones were those which would readily ‘break down’ somewhat, exposing new, fresh abrasive on a regular basis. This is known as friability and was a key concern with traditional clay based waterstones. This friability is what made waterstones cut very quickly, but also caused them to become less flat with use, so much so that the two attributes are rarely mentioned separately, always in the same breath.

“Waterstones are fast, but they dish quickly…”

However, this is no longer entirely true. Not too long ago, a new type of waterstone was developed, those known as ‘ceramic’ waterstones. These stones are generally less friable, and by use of higher quality, more expensive abrasive, they still cut quite quickly. In many cases even faster than the traditional clay based stones. The reputation of these stones is that they are waterstones, but they stay flat. One brand in particular, Shapton with their Professional/Kuromaku stones earned a solid reputation of working quickly and staying very flat during use. But, time and technology marches on, and with these advances came different, more difficult to sharpen steels. Naturally, some waterstones have been developed to cope better with these tough steels, and we now have a third style of waterstone, those which comprise a high quality abrasive with a friable binder allowing them to sharpen very tough, abrasion resistant steels faster than ever before, but we return back to the potential problem of the stone becoming something ‘less than flat’ rather quickly.

Every single waterstone compared in this battery of tests is a compromise of sorts. The manufacturer of each stone has made a decision of where they think the ideal balance of abrasive and binder lies with respect to a specification and/or budget and all of the stones compared (with 2 distinct exceptions) go about their business in a different way to the next.

So, now a picture forms. The previous results only compared speed of each stone, but here we add how flat each stone stayed through its testing. Were the fastest cutting stones sacrificing themselves for speed? Were the slower stones holding back somewhat? And the critical point, which stones really do stay flat?

These charts are based on a calculation. Before initial testing, each stone was measured for thickness. After each test each stone was flattened with the same Atoma #400 diamond plate only until they were flat again, no more and the required number of flattening strokes counted. At the conclusion of testing, each stone was again measured to see how much stone had been used. The total of the missing material divided by the number of flattening strokes required would give a reasonably accurate measure of how friable each stone was in actual use. The number of strokes is not important, nor is how easy each stone is to flatten. All we need to know right now is how much stone was used up to do the job in each test.

Without further ado, the requisite graph.

Note; these figures are derived from the number of passes of an Atoma #400 to remove ALL dishing from each stone after each steel test, divided by the amount of stone consumed during the entire testing session. The divisions are approximately 0.01mm so while the numbers might appear worrying, there is only a very small amount of material consumed over the entire battery of tests.

Now, we have something we might theoretically be able to base some solid judgements upon, especially if you take into account the previous pair of graphs showing how ‘fast’ each stone is. I don’t think it takes a great amount of brain power to see that stones such as the Arishiyama, the 3 Shaptons and the Sigma Power hard seem to be doing a pretty bang up job of cutting quickly yet staying quite flat, or at least not using up much of themselves to get the job done. In fact, the Glass Stone really stands out here, and that’s surprising, even to me.

But there is one steel missing, the white steel torture test…

Ok, now we’re getting serious…

What makes this graph so telling is that because so much work was asked of the stones, those that were more friable or had less durable binder would suffer more than those with a durable binder. At the same time, those with a durable binder but less than ideal abrasive would take a very long time to accomplish this task. But those stones that combine superior abrasive in a friable binder, well, those stones got this ‘torture’ test over and done with rather rapidly, but did give up some of themselves in the process.

Also, because the steel in this test was relatively easy to sharpen Yasuki White #2 back with a modern version of wrought iron, this chisel represents the ‘standard’ chisel most of the stones were designed to be effective with. The soft iron back will also tend to ‘tear’ the surface of the stone, exposing more abrasive and consuming more stone thickness, so while it might appear that a very easy to sharpen chisel would be no real test, the truth is that this test was as severe as possible. For a stone to come through without giving up much of itself, it must be truly dish resistant.

But this is not the entire story.

There are some other factors at play here, and this is where rumour and suspicion start to raise their heads. Many of these stones have a reputation, and some are subject to questionable ‘truths’. In short, from this point on is where myth and fact bump heads and some of these quiet questions that have been asked may begin to be answered.

And yes, some of these results start to take unexpected turns…

It’s going to get ugly, I can assure you of that.

Thanks for reading,


9 comments to Waterstone testing, the results. Part II.

  • Thanks for writing, Stu.
    These articles are very interesting.
    Thank you for the time you spent in the tests.
    Best regards from Italy,

  • Steve C

    Thanks for the info Stu, it’s definitely a subject with a lot of misinformation going around, loving the topic!


  • Kees

    Hi Stu,

    Just a quick question, the Sigma power stone from your store, which on is that in these graphs?
    Just wondering if I bought the right one :-)

  • I only tested the Sigma Power ceramic ‘hard’. The two other Sigma Power stones are the ‘Oribest’ which isn’t listed yet and the Select II which are listed.

    I did not have the soft available to me when I started this testing, and have only recently gotten one. I’m afraid to slip it in because it’s very fast, but also a little ‘dishy’ and looks identical to the hard.

    But within a second of using either stone, you can tell which is which. The hard gets cutting, but it feels hard. The soft bites in and feels very soft.

    Both are good stones, but I find myself attracted to the soft because it feels like sharpening on whipped cream. Just super smooth.


  • Kees

    I still don’t quite get it. Which one do you sell the soft or the hard?
    I ask because I just bought a Sigma 1000 power from you, and would like to know where in the spectrum of stones this one is sitting.

  • Hi Kees,

    The one that is being tested is the one you have, the hard version. I’ve had that one available since the first day the store started.

    The Sigma Power soft #1000 is a new addition, and not yet put through this testing. I now sell both.

    And don’t worry, while the Sigma Hard might not look all that convincing right now, it will do so very soon, starting with the next installment. Trust me on that one.

    I do hope that stone is working well for you too, as it should be!


  • Kees

    Oh, and the stone cuts fast, but I think it tends to dish almost just as quick as my Naniwa 800? I now suspect the flatness of my DTM plate though.

  • Kees

    Just a quick update. I’ve tested the Sigma Power hard 1000 some more with a couple of plane irons. The result is in fact very good. After a lengthy back flattening sequence on a vintage iron, the stone was still perfectly flat form side to side while you could see minimal light under a straightedge in the length. Pretty good and definitley a lot better then my older Naniwa 800 superstone. That one gets thin quickly because of all the flattening. My DMT diamond plate is luckilly completely flat.