Coarse synthetic whetstones: a comparison

After the great success of the three 1k grit stones written by Carlos, we decided to combine our thoughts and stones into another stone comparison. This time, we will review some coarse synthetic stones, as many people are (still) searching for the ultimate low grit stone (fast cutting, good feedback and dish resistant). Of coarse (see what we did there…) this such a stone is a myth, but we hope that this guide will help people to make an informed decision.

The criteria used to compare the stones are some of the characteristics that define a good or bad whetstone. Keep in mind that much of this is subjective and that no rigorous scientific experiments have be done to compare these stones . We will try to give each stones a 1-10 mark with 10 being the best and 1 the worst, but again, this is very subjective and dependent on every person’s reference point. Also, these ratings are only compared to the other stones tested in a specific group, and cannot be used to compare these stones with stones that have a different purpose (e.g. polishing stones).

This review is written by Carlos (KKF handle: valgard, IG: cev_valgard), Otto (Toishigram) and Peter.

King 300, picture courtesy of Otto

The Stones

In this guide, we will compare the following stones listed below. Admittedly, these stones are not all easily comparable due them all having a different grit rating. However, we feel that is nonetheless useful to make some sort of a comparison, so people can make an informed decision. Because of this, we have bundled the stones into a few groups.

In this review, we will abbreviate the stones as follows:

StoneAtoma 140Shapton M24 120 gritSigma 120 gritImanishi 220JNS 300King 300Suehiro Gokumyo Ryu 300Shapton Glass 320Naniwa Chosera 400Shapton Glass 500 double thick
NameAtomaShapton M24SigmaPink BrickJNSKingSuehiroSG320ChoseraSG500
Size (excluding base)210 x 75 x 1mm210 x 70 x 24mmLarge: 205 x 75 x 55mm
205 x 75 x 50mm200 x 65 x 30mm207 x 66 x 32mm205 x 73 x 30mm (25mm soft/5mm hard)210 x 70 x 6mm210 x 70 x 25mm210 x 70 x 15mm

Some notes on splashing and soaking

The SG320 SG500, Atoma, King, JNS, Chosera and M24 are splash and go stones, meaning that they can (and should) be used with a bit of water instantly. The JNS and Chosera however, benefit from a short soak.

The Sigma, Pink Brick, and Suehiro are all soakers. The Suehiro holds water very well as it is a very dense stone, the same can’t be said, unfortunately, for the Pink Brick and the Sigma. Carlos permanently soaks the Pink Brick and still it doesn’t hold water well. Sealing it helps greatly though. The Sigma is even worse for holding water on top which is very annoying, although after sealing it, it can somewhat saturate and hold the water.

A word of advice, use something very thick like a thick epoxy when sealing these type of stones, or the sealant will soak through and create a hard layer on the sides of the stones.

Group 1: Atoma, M24 and Sigma

Speed, dishing, and clogging – All three stones are very fast, but the Atoma definitely has the edge in this category, even more so because the Atoma does not clog while both the Sigma and M24 tend to clog and glaze pretty quickly. This clogging isn’t immediate but the stone needs refreshing every few minutes, with the M24 being the most prone to clogging. In this sense Atoma is much more convenient, especially since the Sigma and M24 should be flattened and refreshed on #36 SiC, and then thoroughly rinsed to avoid contamination and deep 36 grit gauges. An Atoma may be used as well, but it will take a heavy hit.

Feedback – The Atoma takes last place when it comes to feedback, it is simply horrible (and don’t even think about building any convexity)! The Sigma and M24 have very bad feedback, as expected from such a coarse stone, but much better than Atoma. The feedback on the Sigma is better when sealed and the water is held.

Finish and edge – None of these stones are suitable for edge finishing, but can be used to cut a fresh bevel or to grind (remove low spots, change the grind, etc.). Both have a tendency to leave some deep gouges which are difficult to remove on the next stone and can be a problem if intending to polish the bevel, these can be deeper with Atoma, but the Atoma improves in this aspect as it ages (unfortunately at the expense of speed).

Group 2: JNS, King, Pink Brick, SG320 and Suehiro

Speed, dishing, and clogging –  the Pink brick is a fast stone but far too soft and dishes incredibly fast, to the point that average speed is affected by how often you need to stop to flatten. The great amount of mud and fast dishing also mean you have little control over geometry. Overall the worst stone of the whole lot to us.

The Suehiro Gyokumyo has moderate speed and is on the softer side (medium hard, not really soft) and a bit slow on the ultra hard side. It dishes at a moderate pace on the softer side and very slowly on the hard side. There is no clogging on the softer side and it glazes on the hard side relatively quickly.

The SG320 is a fast stone, clogs very fast too and needs quick refreshing, but dishes slowly. The speed of the SG320 shines on hardened steel, it’s quite fast on average on honyaki and mono-steel blades (compared to other stones), but on san mai knives the clogging becomes more of an issue and this affects the overall speed.

The JNS is moderately fast in this range, probably a bit faster than the Suehiro, and dishes at a moderate speed as well. There is very little to no clogging. All in all, this stone is a contender in this category as it is balanced in all three aspects.

King 300 is not the fastest but tolerable on clad and san-mai knives. It’s time you’ll make back by not having to flatten constantly and not having to revisit the lower grits again when later you discover a low that coarse-stone mud from a softer stone had rolled up into and disguised. It seems to benefit from a little Atoma refresh every so often to expose fresh cutting material. Next to hopeless on honyaki. Admittedly it was the über-hard Sukenari flavour but that was quite enough to determine that I don’t want to get this bad boy out for heaving lifting on high HRC monosteel.

Feedback – Best feedback is the Suehiro soft side by a wide margin, it feels even nice, which is crazy for a coarse stone, the hard side feels too glassy and skates, not a nice grippy feedback. The JNS and King have decent feedback as well, with the JNS being more muddy and creamy (and a little bit more thirsty) than the King. The Shapton Glass 320 has pretty decent feedback, a bit hard and has no give but you can still feel it shredding mental when it’s not closed. The Pink Brick dries a bit too fast and it’s too soft for a nice feedback, still, as a muddy stone the feedback isn’t too bad once you have sealed it.

Finish and edge –  The Pink Brick can leave a somewhat OK finish from afar, but it does leave some deeper scratches/gouges, and it’s very prone to get into low spots and hide them rather than remove them. It is almost impossible to flatten a bevel on this stone if that’s your intent; you will end up with some convexity almost by default. It is pretty hard to deburr and get a clean edge on this stone, we wouldn’t recommend for finishing an edge.

The Suehiro’s soft side is ideal for shaping a bevel, it’s an extremely precise stone in both the grit content and how you can shape the bevel. Ideal to give a slight convexity on a knife after rough shaping on Atoma diamond plate. The scratch pattern is very even and you can get a very decent, yet uber toothy edge off the stone. The hard side of the Suehiro doesn’t allow for shaping anything but a flat bevel, unless you like to suffer and struggle a lot. This side is good for cleaning up after the soft side as it finisher higher possibly. The best use of this side is to create a micro bevel, it can leave a super clean edge, crazy for a coarse stone.

The SG320 leaves an OK finish, can occasionally gouge but not common. It is a bit too hard for nice shaping but workable. The edge off this stone can be usable too.

The scratch pattern of the JNS 300 is consistent; we have not noticed any gouging. As it is slightly on the softer side compared to some other stones in this category, it lends itself to shaping of bevels fairly reasonably, but one must be a bit careful of dishing the stone. An edge off this stone may work for knives made of soft steel.

The finish off the King 300 is at best a sort of strafed, steel-wool chic. At worst, a brutal and unflinching reflection of the topography of your blade road on account of its hardness. No sneaky mud rolling up into lows here! Stropped edge can take leg hair shave if done right.[

Group 3: Chosera and SG500

Speed, dishing, and clogging – Both the Chosera and SG500 have good speed for their grit rating, not very fast dishing, and no clogging. All in all, they are very balanced stones. Of course these stones are not suitable for huge thinning or grinding jobs, but they work well for light thinning and removing scratches from lower grit stones.

Feedback – We consider the SG500 to have great feedback, it feels smooth, yet you feel it’s doing it’s work, has just enough give to have a nice feel to it. The Chosera has decent feedback as well, coming close to the SG500.

Finish and edge – The SG500 gives a surprisingly good finish. The edge is very usable, especially for knives made out of softer steel. The Chosera may be a bit too coarse, even for soft knives.


Overall our favourite stone is the Suehiro Gyokumyo , not the fastest of the lot but still fast enough for anything but heavy lifting thinning, great feedback and versatility, great precision and control. It’s a shame this stone has been discontinued though. The second favourite of the lot is the SG500.  If we needed to go with one in each group we would get an Atoma 140, the Suehiro Gyokumyo 300, and a SG500.

Disclaimer – We are not sponsored by any of the sellers or makers of these stones in any shape or form.

3 Replies to “Coarse synthetic whetstones: a comparison”

  1. Nice write up guy’s! Curious what the base level of stone most avg Joe’s should consider? I have an Atoma 140 plate which I use for flattening and thinning (junk knives). Couldn’t imaging setting a proper knife to that course diamond coating,,,,

    I also have JKI 400 soaker in my personal kit, which I like (don’t love), but can’t really imagine going much lower.

    What do you guy’s keep in your personal kits?

    1. Hi Todd, thanks for your kind words! A 400 grit may be on the finer side of things for significant thinning work, but it shouldn’t be problematic if you maintain your knives well (which I assume you do :)). The really low grit stuff like the Shapton M24, Atoma and Sigma are for knives that need a lot of work.

    2. Late reply Todd,
      I have no qualms putting expensive knives to atoma 140 if the work needed is significant enough, but I try to do as little damage as possible. I use most regularly for thinning and shaping the atoma 140, the suehiro gyokumyo 300 or the shapton glass 320 depending on what exactly I’m doing and how much I love the knife, the shapton glass 500, and then jns 1k. From there it depends on what I want to achieve.

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