This is part of a series of blog posts – looking into the appearance and composition of commercially available sharpening stones. If you are interested in the previous episodes, check out the archive for them.

If you have some suggestion on what I should look at next, or want to share your super secret DIY stones, I could be persuaded to open the bag of analytical devices… hit me up on Instagram under @marvgro for that.

Disclaimer: I’m not for sale. Every review you see on this blog is bought with my own money. I have no affiliation to any manufacturer.

Review

I’m always hesitant to review Chinese sharpening stones. I feel like any review is only a snapshot of a moment, a fleeting statement: this was the one I bought, no idea what the next batch will look like, as they are constantly changing, evolving, backtracking in their recipes. The company who made today’s sharpening stone even reached out, offering me a collaboration. I politely refused, and instead ordered this stone with my own money. Let’s dig into Forever Superabrasives Resin bonded diamond Stone – 400/1000 grit. I’ll split the important picture galleries in two parts, some might combine the sides. Please refer to the caption to see which is which.

Let’s take a look under the optical microscope!

Optical micrographs of the (left/first/green) 400 side and the (right/second/red) 1000 grit side of the Forever Superabrasives Resin bonded diamond stone. Instrument: Marvscope

The stone is probably coloured, as the difference between the two sides is quite stark. The coarser, #400 grit side shows an overall green appearance, with some copper coloured agglomerates. The finer, #1000 grit side is more homogeneous coloured, but has large, white-grey particles or agglomerates.

Let’s take a closer look at the #400 side in the SEM:

SEM micrographs of the #400 stone. Instrument: Zeiss GeminiSEM 560.

We can see a plethora of different particles here. The bond itself looks like a phenolic resin bond, based on it’s grumbly appearance. A large amount of small particles is interspersed. We can also make out some voids that look like the contour of bubbles. Grain adhesion doesn’t seem to be super high, as most of the larger grains are already showing some separation from the bond.

Let’s look at the chemical composition! For this we are going to use an advanced SEM technique called EDS. If you want to know more about this, I’ve written extensively about SEM microanalysis here on this blog.

EDS analysis of the stone. Instrument: Oxford Ultim Max  ∞ 40mm² EDS sensor. Note that our EDS sensor doesn’t show elements lighter than boron.

The EDS analysis shows a medium diamond concentration. The large, copper coloured particles seen in the optical micrograph are actually Copper and Zinc – with quite a bit more Zinc than copper. There is also quite a bit of chromium oxide, correlating to the fine particles, but also the green colour of this side. Lastly, the usual SiC that creates the haptic feedback can be found. Overall, mixing looks like it could be improved – while the diamond is distributed quite nicely, as is expected of this particle size – the other components of this bond seem to agglomerate, and break up the regular diamond distribution. Moreover, I do not see why a manual bond would require any metal components – those are typically added for heat conductivity, and there’s not a lot of heat generated at manual speeds.

Let’s take a closer look at the #1000 side in the SEM:

SEM micrographs of the stone. Instrument: Zeiss GeminiSEM 560.

It seems to me like this is a very similar bond- but struggling more from larger agglomerates of fine filler particles. This side also looks to me like it got baked warmer – the phenolic is less crumbly and more solid.

Let’s check out the #1000 grit side’s EDS:

EDS analysis of the stone. Instrument: Oxford Ultim Max  ∞ 40mm² EDS sensor. Note that our EDS sensor doesn’t show elements lighter than boron.

The visual impression from the SEM pictures is confirmed in the SEM. Most of the components from the #400 grit side can be found, but also large amounts of Iron as well as a much higher concentration of sodium. I would guess that the sodium (Na) is maybe some pressing agent, that did not fully debind during initial baking? Very curious. Mixing is a bit worse, which was to be expected – smaller particles are harder to distribute.

In order to evaluate the sharpening performance and material removal mode of this stone, a blade was sharpened with it. I am using a standardised testing procedure, read about it here.  As this is a benchstone, I use a Katocut Nowi Pro to keep the angle constant and get comparable results without much of a human error.

The edge is then analysed in the electron microscope for breakouts and morphological appearance.

First, let’s dig through the 400 grit side – and we’ll start with the harder steel – the M398 blade:

SEM micrographs of the M398 edge finished with the 400 stone. Instrument: Zeiss GeminiSEM 560

Two things stand out immediately to me: Quite a lot of burr, bend over, but also a remarkably smooth bevel at this grit size. The scratch pattern is pretty reglular, with some deeper scratches. The apex is still quite wide – this definitely is the stone to remove material, and not finish a blade. It doesn’t look like the stone is really freely cutting, instead there’s a lot of burnishing, which of course helps with the surface roughness.

Optical micrograph of the M398 bevel. Instrument: Marvscope

The WLI measurement confirms the large burr, and regular scratch pattern:

3D surface height map of the M398 Bevel. Instrument: Zygo NewView 9000, Objective Lens: 20X. Metrological filter chain: LS-Plane to orient data, cutoff 0.1/99.9 percent to remove outliers.

With the surface roughness parameters as follows:

Sa	0.1211	µm
Sq	0.1552	µm
Ssk	-0.4174	–
Sku	3.965	–

ISO 25178 surface roughness parameters. S-Filter: 2.5 µm (gaussian), L Filter: 0.25 mm (gaussian). No F operation besides LSQ leveling.

Let’s take a look at the NitroV edge:

SEM micrographs of the NitroV edge. Instrument: Zeiss GeminiSEM 560

The softer steel is less polished, and the apex quite a bit finer. The stone cuts more easily into it.

Optical micrograph of the NitroV bevel. Instrument: Marvscope

This is reflected in a more irregular surface in the WLI measurements:

3D surface height map of the NitroV Bevel. Instrument: Zygo NewView 9000, Objective Lens: 20X. Metrological filter chain: LS-Plane to orient data, cutoff 0.1/99.9 percent to remove outliers.

Which result in a higher surface roughness:

Sa	0.2022	µm
Sq	0.2674	µm
Ssk	-0.4928	–
Sku	4.637	–

ISO 25178 surface roughness parameters. S-Filter: 2.5 µm (gaussian), L Filter: 0.25 mm (gaussian). No F operation besides LSQ leveling.

Now, let’s see how the #1000 grit side performs!

SEM micrographs of the M398 edge finished with the #1000 stone. Instrument: Zeiss GeminiSEM 560

The large burr formation, even folding over the burr completely, in combination with the surface morphology that shows a lot off miniature burr and prow formation shows that the stone struggles a lot with cutting into the hard M398. It is of course removing material, but also damaging the apex and matrix of the steel here due to the plastic deformation.

Optical micrograph of the M398 bevel. Instrument: Marvscope

Which is further visible in the white light interferometer measurements of the bevel: a diffuse, marred surface:

3D surface height map of the M398 Bevel. Instrument: Zygo NewView 9000, Objective Lens: 20X. Metrological filter chain: LS-Plane to orient data, cutoff 0.1/99.9 percent to remove outliers.

With the surface roughness parameters improved quite a bit compared to the #400 grit side:

Sa	0.0946	µm
Sq	0.1212	µm
Ssk	-0.2354	–
Sku	3.518	–

ISO 25178 surface roughness parameters. S-Filter: 2.5 µm (gaussian), L Filter: 0.25 mm (gaussian). No F operation besides LSQ leveling.

Let’s take a look at the NitroV edge:

SEM micrographs of the NitroV edge. Instrument: Zeiss GeminiSEM 560

The #1000 grit seems to be a quite a bit cleaner in this softer steel. The finish on the bevel is matte, with some irregular streaks caused by rolling grains.

Optical micrograph of the NitroV bevel. Instrument: Marvscope

Overall, the stone has typical , high filler particle resin bond feedback. There’s a certain vibration, firmness that makes it easy to keep a good angle when freehanding. It’s speed is average, the composition and manufacturing could be improved.

The results are okay. We recently had the #1000 grit Edgeworks DMT Resin stone in this blog – all objective parameters point to that one being ever so slightly better, but not decisive.

Price wise, it’s hard to beat this stone – you get diamonds, a decent feedback, in a very affordable (around 120€/$ at the time of this review) package that consists of actually two stones. This stone does get a knife sharp. It does refine the apex and bevel.

The problem is: performance is okay. Just okay, not superb, and objective measurement shows it doesn’t live up to the hype on the internet, pushed forward by cooperations and affiliate links. This leaves a slightly bitter feeling, and I think you can feel in these last paragraphs how disappointed I am.

If you don’t have powder steels, I’d instead get a Shapton Glass. I find the feedback on that one unbeaten – and the results are exceptional homogeneous. It is a little bit cheaper individually, and made by a wonderful company in Japan – with a proven record of quality & consistency.

This is part of a series of blog posts – looking into the appearance and composition of commercially available sharpening stones. If you are interested in the previous episodes, check out the archive for them.

If you have some suggestion on what I should look at next, or want to share your super secret DIY stones, I could be persuaded to open the bag of analytical devices… hit me up on Instagram under @marvgro for that.

Disclaimer: I’m not for sale. Every review you see on this blog is bought with my own money. I have no affiliation to any manufacturer.

Review

Today’s sharpening stone is the finer brother to our last instalment – the Naniwa Diamond Pro 3000 grit.

It is a very pretty stone – an unusual blue colour with a finely bead-blasted aluminium base:

Let’s take a look under the optical microscope!

Optical micrographs of the Naniwa Diamond Pro 3000 stone. Instrument: Marvscope

The stone shows a very irregular appearance in the optical microscope. We can differentiate between (probably) the diamond in green clusters, a blue phase that likely is the coloured binder, some grey-ish phases as well as a couple of very, very red spots. Intriguing!

Let’s take a closer look in the SEM:

SEM micrographs of the stone. Instrument: Zeiss GeminiSEM 560.

The stone shows, quite similar to it’s caorser brother, a standard phenolic bond. The grain adhesion seems to be similar. There are some larger particles visible, but also a lot of micron or sub micron particles.

Let’s look at the chemical composition! For this we are going to use an advanced SEM technique called EDS. If you want to know more about this, I’ve written extensively about SEM microanalysis here on this blog.

EDS analysis of the stone. Instrument: Oxford Ultim Max  ∞ 40mm² EDS sensor. Note that our EDS sensor doesn’t show elements lighter than boron.

The EDS reveals what I already suspected in the optical micrograph – mixing in this stone isn’t particularly well. There are large areas, where the friable Na-Al-F compound where I suspect it is the mineral cryolite (sodium hexafluoroaluminate) absolutely dominates. It seems to be much finer than on the 600 grit stone, but the finer powder clumped together and created some hollow voids where the surface is littered with it. Moreover, we can make out quite the agglomeration of diamond – instead of an even spread, multiple nests of diamond can be made out. There is also again a large amount of SiC, but very, very fine.

In order to evaluate the sharpening performance and material removal mode of this stone, a blade was sharpened with it. I am using a standardised testing procedure, read about it here. As this is a benchstone, I differ from the usual process by using a Katocut Nowi Pro to keep the angle constant. 2 blades are sharpened, one in 65 HRC M398, one in 59-60 HRC Nitro V.

The edge is then analysed in the electron microscope for breakouts and morphological appearance.

Let’s start with the harder steel – the M398 blade:

SEM micrographs of the M398 edge finished with the stone. Instrument: Zeiss GeminiSEM 560

The blade shows a much refined apex compared to the 600 grit stone. The bevel has gotten much smoother, we can easily identify the carbides. Nevertheless, we can still a lot of random direction marring of the surface – very likely caused by the rolling grain accumulating on the stone. I would guess that this is by design – it emulates the feeling of natural japanese stones, where a slush of abrasives builds up, and of course speeds up the stone. Nevertheless, it’s not as clean as firmly bound abrasive, which is reflected in the optical images:

Optical micrograph of the M398 bevel. Instrument: Marvscope

The WLI measurement shows a curious wave like structure parallel to the apex – I’d guess that this is caused by the abrasive slurry?

3D surface height map of the M398 Bevel. Instrument: Zygo NewView 9000, Objective Lens: 20X. Metrological filter chain: LS-Plane to orient data, cutoff 0.1/99.9 percent to remove outliers.

The bevel itself is quite smooth, with the surface roughness parameters as follows:

Sa	0.0471	µm
Sq	0.0635	µm
Ssk	-0.19	–
Sku	4.740	–

ISO 25178 surface roughness parameters. S-Filter: 2.5 µm (gaussian), L Filter: 0.08 mm (gaussian). No F operation besides LSQ leveling.

Let’s take a look at the NitroV edge:

SEM micrographs of the NitroV edge. Instrument: Zeiss GeminiSEM 560

Again, similar to the 600 grit stone, the surface is slightly less polished, with deeper scratches. The optical micrograph shows a very matte, but uniform appearance with a few random deeper scratches:

Optical micrograph of the NitroV bevel. Instrument: Marvscope

The WLI measurement shows again this very curious double wave-structure close to the apex.

3D surface height map of the NitroV Bevel. Instrument: Zygo NewView 9000, Objective Lens: 20X. Metrological filter chain: LS-Plane to orient data, cutoff 0.1/99.9 percent to remove outliers.

The surface roughness parameters have improved, but are a bit worse than on the M398 blade:

Sa	0.0671	µm
Sq	0.0875	µm
Ssk	-0.2729	–
Sku	3.920	–

ISO 25178 surface roughness parameters. S-Filter: 2.5 µm (gaussian), L Filter: 0.08 mm (gaussian). No F operation besides LSQ leveling.

The stone itself still has a surprising amount of feedback for it’s 3000 grit rating. It leaves the bevel with a very matte, diffuse appearance, which is at least to me quite appealing, but a far stretch from a mirror finish. I feel like it is held back by it’s mediocre mixing and the large amount of filler particles. The result is a refinement of the blade, both in surface roughness but also apex width, and I would guess that with some medium duty stropping, one could get a very good edge of this.

Considering that the price of this stone is quite high in my home country of Germany. Unlike the 600 grit, I don’t really like this stone, and I think there are much better alternatives out there.

This is part of a series of blog posts – looking into the appearance and composition of commercially available sharpening stones. If you are interested in the previous episodes, check out the archive for them.

If you have some suggestion on what I should look at next, or want to share your super secret DIY stones, I could be persuaded to open the bag of analytical devices… hit me up on Instagram under @marvgro for that.

Disclaimer: I’m not for sale. Every review you see on this blog is bought with my own money. I have no affiliation to any manufacturer.

Review

I’ve kind of been avoiding today’s sharpening stone – they are after all quite pricey! But, I am very glad I finally got around to it when they were on sale in Germany. Gentle readers, today we are taking a look at the very well reputed Naniwa Diamond Pro in it’s 600 Grit version!

Let’s take a look under the optical microscope!

Optical micrographs of the Naniwa Diamond Pro 600 stone. Instrument: Marvscope

This is going to be an interesting stone. We can see a mixture of a lot of different colours, but also different particle sizes.

Let’s take a closer look in the SEM:

SEM micrographs of the Naniwa Diamond Pro 600 stone. Instrument: Zeiss GeminiSEM 560.

The stone shows a standard, phenolic, grumbly and quite fine resin bond. The grains do not seem to be embedded very firmly – on the top layer, one can make out gaps between the grains and the resin bond. Moreover, there is a large difference in size of the particles: some small, sub 5 micron particles, but also larger particles around 30 micrometre.

Let’s look at the chemical composition! For this we are going to use an advanced SEM technique called EDS. If you want to know more about this, I’ve written extensively about SEM microanalysis here on this blog.

EDS analysis of the Naniwa Diamond Pro 600 resin stone. Instrument: Oxford Ultim Max  ∞ 40mm² EDS sensor. Note that our EDS sensor doesn’t show elements lighter than boron.

As I suspected in the optical micrograph, this stone consists out of several different abrasives. We have the diamond, which shows a medium concentration, but also a slight tendency to clump together. My understanding is that Naniwa uses concrete style mixers, and I have to give them kudos here – I expected much worse. We can see several secondary abrasives (I learned that term from the TSPROF marketing guy to justify their new series parasitic grains, and I am now going to use it to the end of eternity…), mostly SiC which is used as a filler particle (that is the correct term) to increase hardness of the bond, but also some Al-Na-O-F compounds, which is typically the mineral cryolite (sodium hexafluoroaluminate). It helps to reduce loading, but also for the bond to break down and renew the surface. This is one hightech abrasive here, I expected nothing else from Naniwa.

In order to evaluate the sharpening performance and material removal mode of this stone, a blade was sharpened with it. I am using a standardised testing procedure, read about it here. As this is a benchstone, I differ from the usual process by using a Katocut Nowi Pro to keep the angle constant. 2 blades are sharpened, one in 65 HRC M398, one in 59-60 HRC Nitro V.

The edge is then analysed in the electron microscope for breakouts and morphological appearance.

Let’s start with the harder steel – the M398 blade:

SEM micrographs of the M398 edge finished with the Naniwa Diamond Pro 600 resin stone. Instrument: Zeiss GeminiSEM 560

The stone left a slightly marred surface, but for 600 grit this is quite fine. The apex is very straight, albeit not super sharp. I would say for this grit size, this is totally fine and a good result. The bevel itself is slightly marred – one could feel the bond slightly breaking down, and the slush on the surface likely contains a large amount of rolling grains. This is reflected in the optical micrograph, which shows a very matte and diffusely scratched appearance:

Optical micrograph of the M398 bevel. Instrument: Marvscope

Which is further visible in the white light interferometer measurements of the bevel: a diffuse, marred surface:

3D surface height map of the M398 Bevel. Instrument: Zygo NewView 9000, Objective Lens: 20X. Metrological filter chain: LS-Plane to orient data, cutoff 0.1/99.9 percent to remove outliers.

With the surface roughness parameters as follows:

Sa	0.3037	µm
Sq	0.4004	µm
Ssk	-0.7666	–
Sku	4.773	–

ISO 25178 surface roughness parameters. S-Filter: 2.5 µm (gaussian), L Filter: 0.25 mm (gaussian). No F operation besides LSQ leveling.

Let’s take a look at the NitroV edge:

SEM micrographs of the NitroV edge. Instrument: Zeiss GeminiSEM 560

The rolling particles seem to have created a more diffuse and locally pitted surface in the softer steel, whereas at the same time the scratches appear less deep to me.

Optical micrograph of the NitroV bevel. Instrument: Marvscope

Very slight raising of the apex is visible in the WLI images – I would guess that the softer steel is slightly deformed here.

3D surface height map of the NitroV Bevel. Instrument: Zygo NewView 9000, Objective Lens: 20X. Metrological filter chain: LS-Plane to orient data, cutoff 0.1/99.9 percent to remove outliers.

Surface roughness is quite good for such a coarse stone:

Sa	0.2510	µm
Sq	0.3384	µm
Ssk	-1.031	–
Sku	5.741	–

ISO 25178 surface roughness parameters. S-Filter: 2.5 µm (gaussian), L Filter: 0.25 mm (gaussian). No F operation besides LSQ leveling.

Overall, the stone has a pleasant feedback. It is regular, homogeneous and for a resin stone quite hard. The reputation for freehand sharpening is well earned.

The results are totally fine for a 600 grit stone, with good, high-tech composition, decent mixing and abrasive grain density.

I think the only issue one can have with this stone is the (in Germany) quite high price tag for a very thin layer. I heard that they are prone to wearing a bit quicker than other stones, which makes this an expensive stone with a high performance. When you compare it’s performance to a shapton glass for example. I do not think it is justified. Nevertheless, I like it and am absolutely looking forward to trying it’s finer brother soon!