[Review] Naniwa Diamond Stones

[lesslemming]

Dear fellow scholars and students of all things sharp, it has been a while since I posted anything knife related. But recently I found myself with a renewed vigour for sharpening stones.
So here I have a treat for you, if you are unfamiliar with them (and chances are you are unfamiliar with them).

Naniwa Diamond stones.
Expensive.
Rare.
Elusive.

Before we begin, let me set the scene. I have been sharpening knives, razors for almost 20 years now. In my rotation, I employed every Stone Shapton has ever produced, all Naniwa Superstones, Chosera, Imanishi, Sigma Select... the list goes on and on. I have tested (and reviewed in my time) many stones.
All of them had their merits, none were truly bad.

I currently have a full set of Shapton Glass Stones, including the 30k, for my razors. There would be nothing wrong with also using them for my kitchen knives. Alas, I am a weirdo, thus I have a need for a separate set of stones specifically for my kitchen knives. Go figure.
Enter Naniwa Diamond stones.

I have a set of 1k, 3k and 6k. I have no need for the 600 and 400 but I am sure they perform similar to what I am about to describe.
I will present the stones in an inverse progression, from fine to coarse.




General description of Naniwa Diamond stones

All Naniwa Diamond are splash 'n go.
They do not require (extensive) flattening. I strongly recommend a synthetic Chosera nagura to keep the stone clean and reasonably flat.
I have yet to notice real dishing on any of them, after 1yr+ of working with them in a household kitchen environment.
The stones *do* load up. Again, I recommend the Chosera nagura to clean them during extensively long sharpening sessions or when necessary.
The Nagura provided with the stones is, in my opinion, worse than useless.

I use these stones on all my knives regardless of steel/hardness. They just work. Aogami? Yup. Hap40? Even better.

Without being able to draw comparison with other Diamond stones, such as the much more affordable options from Venev,
I can say the Naniwa Diamonds cut clean. Very clean. Each stone feels meticulously designed to follow its predecessor.

In summary I would describe them as Chosera on steroids.

1. Similar feel and equally consistent
2. More cutting surface (75mm width vs 70mm)
3. Works with ALL steels
4. Better polish, finish and cutting speed throughout the range

Are they worth the price? Well, *puts on a lawyer voice* it depends.
There are more affordable options out there that will do just fine.

However, the Naniwa Diamond bring everything to the table that I am looking for:

• Splash'n go
• Luxurious size
• Hassle free, rub them with a Nagura if they need cleaning, don't worry about dishing
• Consistent feel and finish throughout the progression
• Don't worry about exotic steels. The harder the steel, the better the polish the stones leave
• Fabulously rare, yet excellent performance

Naniwa Diamond #6000, cream / yellow color


This stone is the finest in this line-up and honestly, 6k is about perfect for the kitchen. I have finished knives on much, much finer stones, achieving an even more perfect finish.
Yet, nothing is ever truly gained in doing so. To the contrary, I sometimes find myself desiring more bite when I finish on 8k stones and beyond.
The only reason I used to finish on my Naniwa 10k superstone is its impeccable capability to produce a true mirror polish, defying even my magnifying glass enhanced, probing eyes.

The Naniwa Diamond 6k is a hard stone, yet in no way glassy.
There is quite a smooth and delightful feedback which reminds me vaguely of Naniwa Chosera, specifically the 5k.
Despite their hardness they cut fast. Very fast, and their speed is proportional to the pressure you employ (d'uh). I find the Naniwa Diamond 6k to be the ideal finisher, because it leaves a nice and refined edge that retains enough bite to cut all materials equally impressive. It's a mean edge. Keen enough to shave, aggressive enough to cut.

Due to the hardness of the stone and the abrasive employed, the stone leaves what I would describe a very convincing mirror to the naked eye.
I tend to finish with strokes that run parallel to the edge and the Naniwa 6k, as opposed to other stones I encountered in this grit range, leave a very clean looking bevel.
I am hard-pressed to make out the scratch pattern with loupe and direct light, but off course they are present. To the naked eye, it looks almost perfect.

The more than adequate cutting speed allows this stone to double as a highly capable touch-up stone.
Put some water on it, do some strokes and restore an edge to its full potential in seconds, hassle-free.



Edge magnified 10x with direct light source



Impressions of the polish left by the Naniwa 6k on my Konosuke HD2 240mm Wa-Gyuto, Japanese HD-2 steel (semi-stainless)

Naniwa Diamond #3000, blue / petrol color


This stone is an excellent alternative or compliment to the 6k, depending on how you look at it. The 3k is enough to get a used knife back to life. It cuts very well and can be used to polish away some minor dings that happen during use (no chips, of course). It leaves a very nice edge, more than suitable for the kitchen use. Slightly more aggressive than the 6k edge, it will not shave as easily but certainly cut through material with ease.

The petrol coloured 3k feels a little finer than most 3k's I have used; it reminds me of the 3k Chosera. The Naniwa Diamond 3k also cuts similarly fast but leaves a better polish and works better with exotic steels.

The 3k leaves a very convincing polish on hard steels such as Hap40; almost as good as the 6k.
On more normal steels, it leaves a very fine scratch pattern that can still be mistaken for a mirror polish. I have used this stone as a touch-up for my Hap40 knife. It worked very well and left nothing to desire.


Naniwa Diamond #1000, green / grass color


The 1k is clearly meant as a starting point for knives that have been neglected and are in need of sharpening. It cuts fast and feels similar to the Chosera 1k. However, I find it cuts a little more aggressive, yet leaves a clean edge that just feels brutally sharp, yet burr-free (as a 1k should). I find myself bagging the 1k diamond when I visit a friend that has a knife that needs sharpening, as long as I don't expect any re-profiling to be necessary.
It consistently gets the job done.

The scratch pattern this stone produces is clean and homogenous, easily erasable with the Naniwa Diamond 3k.
If you want to impress a friend with how sharp you can make their knife but don't want to pack multiple stones: Pick this one.
I find it leaves a cleaner edge and cuts faster than my worn Atoma 1.2k.

Be advised, though. The Naniwa Diamond 1k will remove metal, especially when used with pressure

 

[mockit]

If I could tell my 3 months ago self something about stones, it would be to buy 3-4 of these (or JKI diamonds) and 2-3 naturals and call it quits lol. You live and you learn. At least learning is fun! Great review.

 

[mk4pi]

have you try it on single bevel knives? I have love and hate relationship with diamond, it's leave the scratch deeper than Mariana Trench even with the high grit one, which i can never seem to be able to get rid off with out have to start polish again from the beginning.

 

[M1k3]

have you try it on single bevel knives? I have love and hate relationship with diamond, it's leave the scratch deeper than Mariana Trench even with the high grit one, which i can never seem to be able to get rid off with out have to start polish again from the beginning.

Are you using diamond plates? Or vitrified?

 

[lesslemming]

have you try it on single bevel knives? I have love and hate relationship with diamond, it's leave the scratch deeper than Mariana Trench even with the high grit one, which i can never seem to be able to get rid off with out have to start polish again from the beginning.

No, I don't own a single bevel. I don't think diamond abrasives are necessarily to blame here. Stray scratches that randomly pop up during later stages can be caused by several things

• Left-over scratches from factory or previous grit
• Contamination of water with grit
• Uneven distribution of abrasive in the stone (agglomeration of grit)
• Third bodies (particles like abrades steel slivers rolling between stone and bevel)
• Stick 'n slip (the knife catches the stone briefly)
• and many others...

All of these issues are accentuated, when the bevel is wide.

If you are referring to unnecessarily deep scratches from coarse diamond stones I suggest starting with a higher grit instead or spending more time on the subsequent one. I usually avoid anything below 1k (for most knives I start at 3k), unless I have to do re-grinds. If I have to do a re-grind, I am prepared to expect some scratches to pop during later stages.

Achieving a perfect, scanning electron microscope* level polish is difficult and usually does not pay off.
The best recommendation I can give is this:

Use 3M lapping film. Especially the diamond ones are amazing.
Those are the only medium that reliably gives me *perfect* results.

BTW. I mean that literally. Over 10 years ago, in my prime, I had access to a scanning electron microscope and used it to check on my blades and progressions. Unfortunately, all the images have been lost. What remains are only images of commercially available razor blades.

Note: image is NOT finished on the Naniwa Diamond stones. This is a razor blade from the brand Astra viewed directly on the edge

 

[mk4pi]

Are you using diamond plates? Or vitrified?

The venev stone the one with F800/1200, i think they are resin base.

 

[M1k3]

The venev stone the one with F800/1200, i think they are resin base.

I have the 400/800 one. I haven't come across deep errant scratches. Maybe you need to condition the surface?

 

[Guirotin]

Wow, thanks very much for this extensive review. I recently bought atoma 400 and 1000 grit stone + 3000 grit naniwa diamond stone. I only used it once, but loved muuuch more the feel on the naniwa than atoma.

 

[captaincaed]

Coming out of the woodwork with a bang. Thank you for the review!

 

[Benuser]

Sorry for reviving the thread. You mentioned a nagura to clean them. I have the #400 and 3k diamond stones. Would the red synthetic Naniwa nagura as delivered with the former Chosera series, #600, work with the diamond stones?

 

[user 52613]

I have the 400/800 one. I haven't come across deep errant scratches. Maybe you need to condition the surface?

The finer grit Venevs have some problems with diamond agglomeration ime.

 

[fortheloveofmoar]

Phenomenal. Very informative thank you!!

 

[Rangen]

Really nice review of some top-quality resin-bonded diamond stones. I have the 600, the 3000, and the 6000. There appears to be a pattern in which the coarser the stone, the less quickly it tends to glaze. So I really only notice it much on the 6000, which is fine, because, like you, I find fewer and fewer uses for it as time goes on.

 

[rob]

Sorry for reviving the thread. You mentioned a nagura to clean them. I have the #400 and 3k diamond stones. Would the red synthetic Naniwa nagura as delivered with the former Chosera series, #600, work with the diamond stones?

Good question, i have the 1000 and used it mostly to sharpen friends stainless German knives.

Initially it was great, cut steel fast leaving a nice clean edge. Although after sharpening 4-5 knives mine is so glazed/clogged it barely cuts and is very slow now.

Have tried cleaning with supplied nagura and also Chosera red nagura neither have helped.

 

[Rangen]

Good question, i have the 1000 and used it mostly to sharpen friends stainless German knives.

Initially it was great, cut steel fast leaving a nice clean edge. Although after sharpening 4-5 knives mine is so glazed/clogged it barely cuts and is very slow now.

Have tried cleaning with supplied nagura and also Chosera red nagura neither have helped.

Interesting. I've done plenty on my 600, and it doesn't glaze fast, and when it does, the supplied nagura makes reasonably short work of the problem.

I don't do much stainless, though, and no softish stainless. I wonder whether that's the difference.

 

[M1k3]

Good question, i have the 1000 and used it mostly to sharpen friends stainless German knives.

Initially it was great, cut steel fast leaving a nice clean edge. Although after sharpening 4-5 knives mine is so glazed/clogged it barely cuts and is very slow now.

Have tried cleaning with supplied nagura and also Chosera red nagura neither have helped.

Rub a coarse stone on it, about 300-500 grit. If that doesn't work, rubbing the stone on silicon carbide around 300-500 grit works also.

 

[Barmoley]

I've had good results with Naniwa Nagura 220. It is SiC and cleans all sorts of stones well for me.

 

[Benuser]

Thanks a lot to all of you. You have convinced me that I may go quite coarse when cleaning my 400 and 3k. So far, a soaked Chosera #600 nagura under a running tap did the job. If ever needed, I now know much coarser is an option as well. Thanks again.

 

[stringer]

I have had good luck with using my Shapton Pro 1000 for nagura on my Naniwa Diamond 600. I sharpen mostly cheap stainless. I have probably sharpened 200 knives on it in the past year or two. Mostly just edge work, very little thinning. I use a coarse crystolon for thinning. No real sign of wear. And it has never clogged. But I nagura it every couple of knives.

 

[Benuser]

Gritwise they must be quite close.

 

[ScharferMax]

Sorry for reviving the thread. You mentioned a nagura to clean them. I have the #400 and 3k diamond stones. Would the red synthetic Naniwa nagura as delivered with the former Chosera series, #600, work with the diamond stones?

I hope I have understood your issue correctly: dislodging embedded residues/unclog the surface/cleaning the stone and restoring its cutting power? If so, then I had a similar issue with some NSK diamond stones. After several tests, I opted for this very hard coarse stone dressing and flattening stone in green carbon, which is really effective, combined with a finer nagura to resurface your diamond stone afterwards. It also worked with my Naniwa 1K diamond. Here's a link if you're interested: https://tetogi.com/collections/accessories-grinding/products/hitohira-round-flattening-stone

 

[Benuser]

I hope I have understood your issue correctly: dislodging embedded residues/unclog the surface/cleaning the stone and restoring its cutting power? If so, then I had a similar issue with some NSK diamond stones. After several tests, I opted for this very hard coarse stone dressing and flattening stone in green carbon, which is really effective, combined with a finer nagura to resurface your diamond stone afterwards. It also worked with my Naniwa 1K diamond. Here's a link if you're interested: https://tetogi.com/collections/accessories-grinding/products/hitohira-round-flattening-stone

Thank you! To be more complete: I got the stones with instructions in Japanese — which I ignore — and without any nagura. Noticed some loading — the situation is far from dramatic — and wanted to know what kind of nagura is safe. With the very different answers by experienced users I've got I'm sure not to damage the stones, and have a lot of options, including yours, when loading would become more problematic — which I hope to avoid.

 

[ScharferMax]

Thank you! To be more complete: I got the stones with instructions in Japanese — which I ignore — and without any nagura. Noticed some loading — the situation is far from dramatic — and wanted to know what kind of nagura is safe. With the very different answers by experienced users I've got I'm sure not to damage the stones, and have a lot of options, including yours, when loading would become more problematic — which I hope to avoid.

You're welcome! It's true that there are many options, but most manufacturers do not offer clear solutions to maintain their own product (except NSK, but their rather expensive flattening stone did not convince me). However, at least my 1K Naniwa Diamond came with a nagura... Regarding the flattening stone I mentioned, I'll send you a DM with a video for demonstration!

 

[Benuser]

You're welcome! It's true that there are many options, but most manufacturers do not offer clear solutions to maintain their own product (except NSK, but their rather expensive flattening stone did not convince me). However, at least my 1K Naniwa Diamond came with a nagura... Regarding the flattening stone I mentioned, I'll send you a DM with a video for demonstration!

Looking forward to seeing it!