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 once again something very special – it’s the wonderfully finished, presented and made FSK Vitrified #1000 Diamond stone. In a previous part, we’ve had the #270 grit of this series, and just like in that review, the finish, packaging and presenting of the stone is fantastic. Be sure to check the #270 out here:

A brief study on sharpening stones – Part 56 – FSK Vitrified #270 (Diamond, Vitrified)

Just like the #270 grit, this is really expensive premium stone – with taxes and import duties, it was just above 600 Euro, delivered to my doorstep in Germany.

Let’s take a look under the optical microscope!

Optical micrographs of the FSK vitrified #1000 diamond stone. Instrument: Marvscope

The stone is a lighter colour than it’s #270 grit brother. Less of a green appearance, which is usually typical of finer diamond grits. The stone is nearly transparent, with a high degree of vitrification in the bond.

Let’s take a closer look in the SEM:

SEM micrographs of the FSK vitrified #1000 diamond stone. Instrument: Zeiss GeminiSEM 560.

The surface is very regular, and once again shows small bubble like voids. The diamond grit is distributed all over, with a blocky, high quality diamond predominant. FSK seems to use very high quality raw material to make this stone! The diamonds are firmly embedded in the bond, and the actual vitrified matrix looks extremely dense and compact.

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 FSK Vitrified #1000 diamond stone. Instrument: Oxford Ultim Max  ∞ 40mm² EDS sensor. Note that our EDS sensor doesn’t show elements lighter than boron.

EDS analysis shows a super regular distribution of the diamond. Concentration should be a bit higher if you ask me, but the mixing seems to be absolutely top notch. It feels like I’ve seldom had such good distribution on a diamond stone.

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. Nevertheless, it’s 65 HRC M398, and sharpened to 17 DPS with resin bond diamond stones down to 10 µm. Afterwards, the tested stone is used, first in a back and forth movement until the surface becomes homogenous, and then alternating, edge trailing strokes (5-5-3-2) on each side, for a total of 20 strokes towards the apex per side. No pressure is applied but the weight of the apparatus. Moreover, the same approach is repeated with a blade in NitroV at 59-60 HRC.

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 FSK vitrified #1000 diamond stone. Instrument: Zeiss GeminiSEM 560

The bevel has a slightly toothed edge, with a clearly folded over (facing away from the viewing direction) burr. The bevel surface morphology is super regular – there’s close to no deep scratches.

This is further visible in the optical micrograph: A toothy edge, that is super homogeneous albeit matte in it’s appearance.

Optical micrograph of the M398 bevel. Instrument: Marvscope

The WLI measurements show this exact situation. The blade is diffuse, not super smooth, but very regular. A large, multi micron burr exists on the apex.

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 surface roughness parameters reflect this. It is an acceptable surface roughness for a #1000 stone.

Sa	0.2741	µm
Sq	0.4098	µm
Ssk	-0.4744	–
Sku	11.90	–

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 NitroV bevel, shows a larger burr, but also an even more homogeneous surface. I actually love the matte, diffuse finish created here. There are quite a few much deeper scratches, but again they are so well distributed that they don’t really mar the surface.

The large >10 µm burr is visible in the optical micrograph as well:

Optical micrograph of the NitroV bevel. Instrument: Marvscope

And facing upwards in the WLI interferometric picture, we can really see that it is nicely bend over. This is an easily detectable burr, which definitely needs to be removed before a sharp apex is achieved.

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 deeper scratches are reflected in the quantitative surface roughness parameters:

Sa	0.6563	µm
Sq	1.069	µm
Ssk	0.4803	–
Sku	14.61	–

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

The stone itself is blissful to use. It’s got fantastic feedback, is very hard, doesn’t seem to wear at all, requires next to no soaking, just regular reapplication of water. I know this stone was hyped as a wonderful freehand benchstone on the internet, and I can definitely understand it. It is well made, the results are decent, the finish is immaculate if one wants a matte, diffuse surface. I only feel that the burr created is too large for this grain size. The major downside is the limited availability and high price. It kind of feels like one can get a similar result from a sharpening stone 5x cheaper, albeit without the wonderful design, packaging and vitrified feel.

I like this stone and just like the Shapton glass, it will become a regularly used sharpening stone when I partake in sharpening as a hobby!

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. This review is about a product I’m selling, so you can consider this an advertisement where the local jurisdiction requires me to state this.

Review

Today we’re going to take a look not at a stone, but something that goes on a stone. By popular demand, I proudly present: Dr. Marv’s Wunderlubrikant.

Since I started my own sharpening stone series, the number 1 most asked question was what lubrikant to use with it. I typically answered with “any high quality honing oil will do”, but the one sold by hapstone seems to be horrible, and industrial ones are very hard to source as they are not meant for B2C series. To answer this demand, I worked together with my good friends from the German high tech lubricant company oelheld to get all the legal stuff done so I could sell bottles of the “Wunderlubrikant”. It really was a massive effort, and I also don’t really like selling and stocking oil, so this is first and foremost a service to the sharpening community. When I started in sharpening, I tried many of the “home use” liquids suggested by the communities, but also a lot of industrial high tech solutions. What one wants from a lubricant in hand guided sharpening is the following:

1.) Reduce loading on the stone

2.) Bind the swarf so it’s not becoming an aerosol

3.) Ideally help with the cutting action and improve surface finish / lower surface roughness

In order to test and benchmark, I sharpened with 3 brandnew 30 µm diamond stones (my own resin stones). One was used with soapy water, one with mineral oil and one with the Wunderlubrikant. A decent layer of the lubricant was added. In the case of soapy water, the application was re-applied every 50 strokes to combat it running off and evaporating. The stone never got dry.

Applied coating of the “wunderlubrikant” on the 30 µm stone.

Each stone did 200 strokes on the brandnew, dressed stones. A picture of the stone surface before and after wiping it off vigorously with a tissue was recorded. This shows the tendency to load.

Photographs of the “stone loading test”. 200 strokes on M398, with a layer of the tested lubricants applied. Residue after wiping off and the tissue used.

I do believe the images speak for themselves – the tendency to load is massively reduced through the Wunderlubrikant. The all time classics fall very much short.

Afterwards, I dressed the stones anew and then sharpened 3 NitroV blades. Here, I first used the 30 µm stone with the lubricant to completeley remove the scratch pattern from the previous stone. Then I changed the movement angle of the stone (by about 60°) and did 100 strokes. This is to show both the surface finish, but also the “speed” at which the stone is working. Ideally, no scratches form the previous movement direction are visible, and the bevel is smooth. The blades were analysed via scanning electron microscopy, but also the bevel roughness measured with our fantastic Zygo white light interferometer.

Let’s start with the Wunderlubrikant:

SEM micrographs of the bevel surface after sharpening with the Wunderlubrikant. Instrument: Zeiss GeminiSEM 560

The bevel sharpened with the wunderlubrikant shows a super regular, very even appearance. Macroscopically, the tracks left by the individual grains go over the full FOV. Zooming in even further, a very smooth surface with a low tendency for ploughing or burr formation is shown.

3D surface height map of the NitroV Bevel sharpened with the Wunderlubrikant. Instrument: Zygo NewView 9000, Objective Lens: 20X. Metrological filter chain: LS-Plane to orient data, cutoff 0.1/99 percent to remove outliers.

The 3D height map shows this as well: a very flat, even bevel. There is no noticeable falloff or convexing of the bevel.

Of special interest is the surface roughness:

Sa	0.0402	nm
Sq	0.0564	µm
Ssk	-0.3263	–
Sku	6.515	–

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

The surface values already approach a polished surface – a certain gloss is visible on the blade.

Optical micrograph of the NitroV bevel sharpened with the Wunderlubrikant. Instrument: Marvscope

Next, let’s take a look at the soapy water. It is after all the lubricant probably everyone has at home!

SEM micrographs of the bevel surface after sharpening with the soapy water. Instrument: Zeiss GeminiSEM 560

The surface is marred by some residual scratches from the previous grinding direction. Moreover, the surface shows at 5kx magnification some signs of plowing of the grain. Instead of cutting through the material, plastic deformation happens – the surface is sligthly burnished, and thus produces these flowy prows on the side of the tracks. Some deeper scratches are also visible.

3D surface height map of the NitroV Bevel sharpened with soapy water. Instrument: Zygo NewView 9000, Objective Lens: 20X. Metrological filter chain: LS-Plane to orient data, cutoff 0.1/99 percent to remove outliers.

Surprisingly, the bevel shows some convexing towards the apex! This is only about 2 micrometre in height, but quite suprising to me. Moreover, the surface roughness is significantly higher (about 2x):

Of special interest is the surface roughness:

Sa	0.1046	µm
Sq	0.1513	µm
Ssk	-1.618	–
Sku	6.982	–

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

The optical micrograph supports this: The apex was hit, but some residual scratches from the previous movement direction are clearly visible. Overall, because of the loading, the material removal speed sharply dropped.

Optical micrograph of the NitroV bevel sharpened with soapy water. Instrument: Marvscope

Last but not least, the mineral oil. Mineral oil is popular, because it is available in a “food safe” version. I’m not sure why people are so focused on that property – don’t you wash your knives after sharpening?!? I personally don’t want to eat swarf 🙂

SEM micrographs of the bevel surface after sharpening with mineral oil. Instrument: Zeiss GeminiSEM 560

The surface shows the same, irregular residual scratches as the bevel from the soapy water did. Moreover, we have some random, deep scratches that look like they were created by rolling debris/grains.

3D surface height map of the NitroV Bevel sharpened with the Wunderlubrikant. Instrument: Zygo NewView 9000, Objective Lens: 20X. Metrological filter chain: LS-Plane to orient data, cutoff 0.1/99 percent to remove outliers.

This is further confirmed in the 3D height map, where a slight convexing (about 1.5 micrometre) is also visible. Moreover, the cutting edge is quite ragged.

The surface roughness is lower than with soapy water, but higher than with the Wunderlubrikant.

Sa	0.07706	µm
Sq	0.1100	µm
Ssk	-1.113	–
Sku	6.712	–

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

The random scratches are easy to make out in the optical micrograph. Because of their random direction, but also the SEM morphology, they seem to be rolling debris or loosened grains.

Optical micrograph of the NitroV bevel sharpened with mineral oil. Instrument: Marvscope

I hestitate with a conclusion, because the differences are so dramatic, so clear, and this is my own product. I can already hear people scream “he just wants to push people to buy his product!!!1111”. Frankly, I am very happy with NOT shipping individual bottles of oil all over the planet. It’s a massive pain to bottle oil manually, and the German legislation on bringing a liquid on the market is so obscure, that the effort in getting this done will never make this a profitable product. Nevertheless, every review gets a conclusion:

The Wunderlubrikant showed a significant, superior result: Not only was loading massively reduced and easily wiped off. The removal speed was by far the highest, the bevel had the lowest roughness, cleanest cutting action and nicest surface morphology.

Soapy water had the worst loading – so much that I would probably recondition the stone after every 2 bevels, something I do with my regular, Wunderlubrikant applied stones every few months. The surface roughness was high, and clear smearing/plastic deformation was visible.

Mineral oil sits somewhere in between, but still falls significantly short, especially in terms of loading on the stone.

If you allow me to expand why Wunderlubrikant performs this well:

An often overlooked property of lubricants is the load bearing. This is the phyiscal property on how much pressure leads to a collapse ( = rupture) of the oil film. A good lubricant acts like miniature “bearings” around the cutting edge – allowing the abrasive to cut, instead of smear, and reduce friction. This only works, if the lubricant can stay on the abrasive grain as a, few molecules thick layer, even under the pressure of the sharpening/grinding action. The Wunderlubrikant is a specifically designed high tech MQL oil on an ester basis. It’s highly lubricating, but also has a fantastic load bearing property.

Oh, and regarding safety:

I’ve exposed my stones for several months to the Wunderlubrikant. Moreover, most of the stones in this blog were reviewed with this specific lubricant. No delamination, deconstruction or damage to any resin bonds has been observed.

This product is non-hazardous and does not meet the criteria for classification as a dangerous good under GHS (Globally Harmonized System) regulations, IATA, IMDG, or ADR standards. It requires no special handling, contains no restricted substances, and is intended for personal use. Because of this, I can even ship it internationally. Because it’s ester based, it even washes off without residue with water. No solvents needed.

Still, I wouldn’t eat it if I was you.

Dr. Marv’s Wunderlubrikant is available in my online shop:

Dr. Marv’s Wunderlubrikant

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 another Jende resin stone. We’ve had it’s larger brother, the 120 µm on this blog before – check it out here.

This episode, we’ll dig into the 30 µm stone. It’s a light colour, showing a mixed-abrasive appearance to the naked eye.

Let’s take a look under the optical microscope!

Optical micrographs of the Jende 30 µm resin stone. Instrument: Marvscope

The stone itself shows quite the irregular composition – there’s areas that are more yellow-ish in colour, some very white spots, but also black particles interspersed. Moreover, even before use, the stone feels very friable – rubbing your finger along it, it has a lot of feedback and bite, but just doesn’t feel fully solid.

Let’s take a closer look in the SEM:

SEM micrographs of the Jende 30 µm resin stone. Instrument: Zeiss GeminiSEM 560.

The stone has a lot of abrasives grains in it – there’s certainly some diamond, but also some oxide particles in different sizes visible. The diamond particles don’t really look very homogeneous in size – I’d postulate from the pictures that this stone exhibits a quite large spread in particle size.

Some grains show clear delamination from the binder already – very curios! Remember, this is always before actually using the stone.

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 Jende 30 µm resin stone. Instrument: Oxford Ultim Max  ∞ 40mm² EDS sensor. Note that our EDS sensor doesn’t show elements lighter than boron.

The stone itself is a mix between diamond particles – the feeling that the size differs wildly is confirmed here. Particles approach nearly 50 microns at the upper end, but there is also diamond particles in the sub 10 micrometre size. The distribution of the diamond is less well done than on the 120 µm stone, too. Moreover, the stone has large and small ceramic particles in it, of different species. There is some Mg-Si-O, but also some pure Al2O3 particles. Again, there’s quite a bit of sodium particles – very curious! The stone overall is a colourful one, with lots of different elements in it. Pretty!

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. Nevertheless, it’s 65 HRC M398, and sharpened to 17 DPS with resin bond diamond stones down to 10 µm. Afterwards, the tested stone is used, first in a back and forth movement until the surface becomes homogenous, and then alternating strokes (5-5-3-2) on each side, for a total of 20 strokes towards the apex per side. No pressure is applied but the weight of the apparatus. Moreover, the same approach is repeated with a blade in NitroV.

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

The stone itself exhibits an exorbitant amount of feedback – but is super friable. Even after just a couple of strokes, it starts to form a slurry of abrasive particles on the blade. This slurry of course boosts material removal rate -but the rolling abrasive grains also mar the surface. Moreover, when wiping off the residue, there’s a high chance to scratch the blade, and if one doesn’t clean it properly, there’s certainly the chance to contaminate subsequent sharpening stones with the residue particles.

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

SEM micrographs of the M398 edge finished with the Jende 30 µm resin stone. Instrument: Zeiss GeminiSEM 560

The surface shows clear signs of that friable stone nature – the surface morphology is dominated by pitting, burrs and prows on the bevel. Moreover, the apex is not really refined nor much finer than on the 120 µm stone. A large number of black particles embedded into the blade can also be made out – these are typically in the sub 5 µm range.

This translates into a very matte look for the bevel, and a toothy edge:

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.

On popular demands (thanks to Branislav for requesting this!) I’ll include surface roughness parameters for the bevels:

Sa	0.3792	µm
Sq	0.5065	µm
Ssk	-0.7194	–
Sku	4.913	–

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 shows even more signs of plastic deformation through large rolling grains. There’s also deeper scratches, as the softer matrix doesn’t resist the larger ceramic oxide particles as well as the M398 steel does.

A much higher number of black particles made me curious – so I bumbed the voltage of the SEM and did another SEM analysis, this time focused on one of these particles.

The curious black particles we find embedded into the blade are pieces of diamond, that because of the friable nature of the sharpening stone are rolling around, and then embedding into the blade:

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

The surface sometimes also shows much deeper scratches – I would imagine this comes from a > 30 µm particle becoming loose and dragging through the surface before going over the edge and accumulating on the second side of the bevel.

Optical micrograph of the NitroV bevel. Instrument: Marvscope

WLI confirms the existence of deeper scratches on this bevel:

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.

With the surface parameters also taking a small dip and being slightly coarser/rougher:

Sa	0.4167	µm
Sq	0.5606	µm
Ssk	-0.9312	–
Sku	5.064	–

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

Overall, this is a quick acting stone. If you have tried adding abrasive paste (for example CBN paste) to a stone before, you have experienced that loose abrasive really boosts material removal rate. At the same time, at 30 micrometre, properties I look for edge refinement, removal of scratches and general increases in sharpness. Because of the highly friable nature of this stone, bad grain adhesion, insufficient mixing, mediocre particle size control and large ceramic oxide particles in it, the performance of this stone is overall very mediocre.

I think at this price point, there are plenty of higher performing alternatives out there. A pity, because the feedback for sure is nice!

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 new KMFS Diaresin stone. I’m a bit jealous – diaresin is a really cool brand name for a sharpening stone! KMFS is well known for their sharpening devices – I’ve had reviews of their mechanisms on the blog before (Vantaedge and the Sensei).

Let’s take a look under the optical microscope!

Optical micrographs of the KMFS Diaresin #1000 stone. Instrument: Marvscope

The stone has an intense, green colour. It’s not super homogeneous in the colour, and because it’s a relatively coarse stone, even at low magnification, the diamonds can be made out. The resin itself is quite crumbly – we can see there’s not a lot of sintered interconnection between the particles, even at low magnifications.

Let’s take a closer look in the SEM:

SEM micrographs of the KMFS Diaresin #1000 stone. Instrument: Zeiss GeminiSEM 560.

The SEM shows that not only are there major block particles on the stone, but also a covering of very fine, sub micron particles in the mix. Inside the stone matrix, we can make out a decentl distribution and also decent concentration of diamond grains, but also other, sligthly larger grains. The stone in itself is not super homogeneous, there are some regions that look a bit different to the overall structure.

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 KMFS Diaresin #1000 stone. Instrument: Oxford Ultim Max  ∞ 40mm² EDS sensor. Note that our EDS sensor doesn’t show elements lighter than boron.

Elemental analysis confirms the decent concentration of diamond. Moreover, the stone contains a large number of silicon particles – I’m not 100% sure why no other elemental channel appears in the regions where silicon is predominant, I would have expected the grains to be either silicon carbide or silicon oxide – pure silicon would be a very novel choice as an additive filler for a sharpening stone. Maybe the manufacturer has some idea? I do know that he is an avid reader of this blog 🙂

There is also an explanation for the bright green colour of the stone – the small, sub micron particles appear to be chromium oxide. Last but not least, a small amount of sodium oxide rich particles are distributed over the stone. The EDS analysis can’t detect hydrogen, so it’s unclear whether this really is soda – again, a curious result in a non-ceramic stone.

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. Nevertheless, it’s 65 HRC M398, and sharpened to 17 DPS with resin bond diamond stones down to 10 µm. Afterwards, the tested stone is used, first in a back and forth movement until the surface becomes homogenous, and then alternating strokes (5-5-3-2) on each side, for a total of 20 strokes towards the apex per side. No pressure is applied but the weight of the apparatus. Moreover, the same approach is repeated with a blade in NitroV.

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

During the sharpening action, the stone exhibited a lot of feedback. While it is quite hard in the sense that it is difficult to cut into the stone, it is also crumbly and slowly disintegrated, creating a swarf/debris, similar to how one gets on a natural stone. This increased the feedback, and gave the sharpening motion a “gritty” feel. Fun fact: according to the manufacturers homepage, it’s fine to use this stone with WD-40!

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

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

The stone left a very matte finish on the blade. Lots of small micro serations and burrs are apparent – the apex itself is very burr free but also rounded over. There are some loose diamonds which have embedded themselves into the steel matrix; this was expected seeing how the stone created an abrasive debris slush during the sharpening action.

Optical micrograph of the M398 bevel. Instrument: Marvscope

The optical micrograph confirms this – a very matte, very regular appearance. The edge is sligthly toothy.

Let’s take a look at the NitroV edge:

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

While the NitroV bevel also shows burrs and prows along the bevel, and definite signs of diamond particles that rolled and imprinted, the overall finish is sligthly better in the softer steel. The apex is also not super sharp, but less rounded over than on the M398 blade.

Optical micrograph of the NitroV bevel. Instrument: Marvscope

The bevel here is once again homogeneous, and slightly toothed.

Overall, the stone leaves me with mixed feelings. It’s a thick stone, but slightly thinner than the market standard (22 mm wide vs 25 mm). Feedback is okay, and the sharpening result is within the expectation for a 1000 grit stone. I think it could be majorly improved by better sintering, to give it better grain adhesion and a slightly firmer structure. The addition of chromiumoxide makes it pretty, but doesn’t really add anything to the result. The stone itself is very affordable, at the time of this review it was sold below 40 €. This makes it an absolute bargain. KMFS is, just like with their sharpening mechanisms, continuing to bring affordable products to the market. I can only applaud that!

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 Jende Resin 120 µm. I have no idea why it took me this long to get around making a review of a Jende stone – I even got asked by avid readers whether I have some conflict with them. Honestly? They never were on my radar, but by popular request (which in turn raised my interest) I ordered some. Jende is an american company and has been making sharpening equipment for quite some time already. My order shipped from their Taiwan factory, which is a pity – I had hoped that an American company would actually produce in America, but I guess this is not the case for the full range of products they offer.

Let’s take a look under the optical microscope!

Optical micrographs of the Jende Resin 120 µm stone. Instrument: Marvscope

The stone is a curious, yellow colour. It’s fixed to a steel blank, making the whole abrasive very heavy. We can make out parts that are very flat and even, and others where the stone looks a bit more porous. The diamonds appear very white in colour – this is quite curious, as most diamond powders are actually slightly greenish in colour. The size in optical micrographs looks to be a bit on the smaller size, but I always find it very difficult to correctly measure resin stone diamond sizes optically, as the resin covers the stone partially and contrast to the resin is also horrible.

Let’s take a closer look in the SEM:

SEM micrographs of the Jende Resin 120 µm stone. Instrument: Zeiss GeminiSEM 560.

The stone has quite a few different sized abrasives in it. We can make out large, flat chunks, but also many smaller, blocky, angular grains here. There’s quite a few voids, which have a “glassy” or smeared appearance to them – a sign that these are pores from the manufacturing process, and not lost grains. The resin itself looks like a phenolic type resin, with a very small, gritty look to it.

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 Jende Resin 120 µm stone. Instrument: Oxford Ultim Max  ∞ 40mm² EDS sensor. Note that our EDS sensor doesn’t show elements lighter than boron.

The EDS analysis shows that the large, flat particles are actually the diamond. They are well within their nominal size – so the appearance on the optical microscope was, as I postulated, misleading. From a chemical composition point of view, we can make out the diamond in some clusters – mixing could be a little bit improved if you ask me. The smaller, blocky abrasive grains are aluminium oxide – and they are very well distributed all over the stone, as well as much smaller than the diamond grit. There will be future reviews on finer Jende stones, it will be very interesting to see whether the Al2O3 is the same size throughout the series.

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. Nevertheless, it’s 65 HRC M398, and sharpened to 17 DPS with resin bond diamond stones down to 10 µm. Afterwards, the tested stone is used, first in a back and forth movement until the surface becomes homogenous, and then alternating strokes (5-5-3-2) on each side, for a total of 20 strokes towards the apex per side. No pressure is applied but the weight of the apparatus. Moreover, the same approach is repeated with a blade in NitroV.

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 Jende Resin 120 µm. Instrument: Zeiss GeminiSEM 560

Overall, the stone did a decent job. The apex is refined, albeit not insanely sharp. Material removal was quick and consistent. The bevel surface structure shows a mix between real cutting action as well as ploughing of the grains, forming some micro prows and burrs. Some deeper, random scratches are visible.

Optical micrograph of the M398 bevel. Instrument: Marvscope

I’ve recently gotten access to a wonderful white light interferometer – a Zygo Newview 9000. I’ll try, as time permits, to include 3D scans of the bevel in future reviews, starting with this one:

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.

We can see the impression from the SEM pictures validated, but also get some quantifiable numbers. The deeper scratches are in a low, single digit micrometre range. I would say this is a decent result here, and something that can easily be fixed by the progression of grits.

Let’s take a look at the NitroV edge:

SEM micrographs of the NitroV edge finished with the Jende Resin 120 µm. Instrument: Zeiss GeminiSEM 560

The softer steel with a lower carbide content shows a higher amount of deep scratches. Moreover, the apex is not very well defined, with a ragged line over the whole blade. Some cracking near the apex can be spotted on the more detailed pictures.

Optical micrograph of the NitroV bevel. Instrument: Marvscope

The optical micrograph confirms this. Larger breakouts, up to several 10 µm are visible. The bevel overall has a less consistent appearance. Some burrs can be detected out of the focus plane.

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 3D surface data further confirms this: we can see some deep scratches, reaching into the 10 µm range. Also, more scratches at 90° to the predominant scratch direction are visible. This is very interesting, as I vary my sharpening approach by this angle: I typically start at an angle 45° to the apex, until all the grinding marks from the previous stone are gone. Then I switch direction by about 90° – so that the grinding marks once again are 45° to the bevel, continue until all grinding marks are gone and then go to my testing procedure of alternating strokes on each side. Overall, that’s typically at least 100 strokes per side – that a deep groove “survives” to be visible is quite astonishing. I would guess that this is either caused by loose, rolling grains or maybe by some agglomerated nests of diamonds.

Overall, the Jende resin stone is a decent stone. I found the feedback pleasant, although the stone stinks really badly right out of the box. Material removal is consistent after an initial drop of, it’s quite fast and a good choice to set the initial bevel. It has strong competition in it’s price range – especially by the Ukranian sharpening stones from PDT. If you are looking for a more high quality option, there are some around on the market.

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 review is a “mini” one – and it’s only looking (doing microscopy!) at the carrier of abrasives, namely the Jende nanocloth. It’s an artificial strop, and when I first read about them, I was wondering what these would be like. It’s a mini review, as I won’t use it to sharpen or strop an edge – maybe in a future episode of the stropping series.

The strop comes on the Jende-typical brushed finish steel blank, where it sits on a thick polymer base. This gives the whole strop quite a bit of weight – I’m unsure whether that’s a good decision for a flexible strop! The actual nanocloth is quite thin:

Let’s take a closer look under the microscope. The lower frequency of posting these past two months is twofold – I’m very busy with development, but also wanted to upgrade my optical microscopy. I went down the “DIY” route, and probably spend more than I should have, and also more than I probably would have paid for an upgrade over our Leica Emspira. Ah well! Feast your eyes on high resolution optical images:

Optical micrographs of the Jende Nanocloth. Instrument: Dr. Marv-Scope

We can make out a very regular, high porosity material. It exhibits a dense matrix around some pores – the pores themselves are very evenly spaced.

Let’s take a look under the SEM:

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

The view under the SEM is similar – we can make out cylindrical, very straight recesses that go quite deep! I’ll have to revisit this once I coat it with diamond emulsion. Seeing how the voids are > 30 µm in diameter, I wonder what will happen to diamonds – will they just accumulate inside these voids, or also sit on the polymer matrix?

This is the second instalment of a new blog series, where I try out sharpening mechanisms. I’m not yet fully sure about the format – I will write about things that matter to me, such as build quality, capability to sharpen, but also very subjective things like how it feels to sharpen with this. If I was you, I would expect this to be a rare blog segment. The reviews will be independent from the manufacturer, without control over what I test or write. I am not paid nor do I receive anything from the manufacturer if you decide to buy one.

If you make a sharpening device and you want me to test it, feel free to reach out.

KMFS Sensei

Today’s sharpening mechanism is made by the Czech Company KMFS. In the last review, we had their 1×6″ mechanism – this time it’s the device meant to aid you with benchstones!

At the time of this review, the mechanism retails for about 500 Euro. The device was a loaner unit given to me by the manufacturer, but they had no control over this review and didn’t see it before it was uploaded publicly.

The KMFS Sensei, assembled with the infinity angle adjuster.

The device gets delivered in a custom foam cutout, very sturdy yet compact case:

It assembles in just seconds – pretty much the only thing you have to do is put in one single screw to secure the base to the vertical stand. The case has enough space so one could fit some sharpening stones in there – making it a very mobile setup.

Build Quality

Let’s take a look around it:

The device is clearly a vantaedge – silver metal parts, milled finishes, a combination of steel and aluminium. It is quite compact – barely longer than the 200 mm benchstone. The guiderails are from steel, the bearings are easy to move and the whole device has a heavy, solid feel to it. Because the lever from the swinging guiderail gets quite large, there are some detacheable little feet (visible close to the vertical rod at the back), that just “clip” in. Overall, the whole device is very quickly assembled.

I think it’s a good look for the device, very fitting. A black edition would be superb though, especially together with the brass nut!

KMFS is a European company located in the Czech Republic and manufactures, as far as I know, the parts themselves. This is something I can highly appreciate – kudos, KMFS!

The Sensei came out relatively recently, and you can see that the manufacturer is trying to keep not only a style, but also some shared parts. The loaner unit I have comes with the new “infinity” adjustable angle mechanism:

Detail photos of the infinity adjustable mechanism.

The infinity adjuster is pretty cool: A thumbscrew drives a little gear that changes the angle. There is a rough indicator in the back, but the exact angle is set best via a small, digital angle cube. The knife is held very securely by two strong magnets that have a rubber cover. Everything is screwed together and should be user replaceable – for example, if worn out. Moreover, this allows for upgrading the device – my understand is, it typically comes with a couple of pre-set angles, and the infinity adjustable mechanism is an addon. I would imagine the manufacturer will come out with more possible addons, maybe a clamp, in the future, so it’s nice that it’s not pressed/glued together.

The mechanism itself is self-locking – which is pretty neat in itself, as it does not require to tighten something. Nevertheless, there is a slight amount of play/backlash in the whole gear system, which you can make out near the end of the video. I think this is acceptable – after all, gravity preloads the system!

The device as something really cool in the base – basically, the whole base is the sharpening stone clamping utility. This makes it very solid, and the manufacturer has included some nice touches. For example, there is a black, plastic (I’d guess POM!) support that slides along the rails. The two jaws that clamp are milled from durable steel, and feature a small dovetail – this is super clever, as it then easily accepts smaller 1×6″ sharpening stones.

Clamping mechanism of the KMFS Sensei – milled from stainless steel, with a dovetail that accepts the popular 1×6″ stones.

Why do I love this so much? You see, I have a super large collection of 1×6″ stones. And I’d say that probably, for experimenting, there are more different, curious, novel 1×6″ stones out there than benchstones. The typical rubber benchstone holders don’t accept those – but the Sensei does!

Sharpening action with a smaller 1×6″ stone on the device.

Sharpening Process

Sharpening on the KMFS Sensei is very nice. Because of the low moving mass (the guiderails just swivel around their pivot, so the moving mass is pretty much the knife & vertical rod / sled), there is not a lot of resistance.

Swapping sides requires to overcome the magnetic force – this is something that’s very easy on a larger knife, as one has a larger lever, and a bit tricky on the small Kasé Shard I am using here to demonstrate it. The motion is very smooth and without noticeable friction.

For the overall geometry/working principle of this type of sharpeners, I would like to refer you to the previous two parts of this series – there, I explained it in detail! Basically: you are constraining the blade via the locked angle, so that you get a repeatable process. Because the vertical rod has the whole mechanism floating, you don’t have to compensate for stone height. This is especially nice at later, finer grit progressions.

Just like I stated in the Katocut Nowi Pro review: The motion used here is what I think sharpening is meant to be – it just feels natural. But, and it’s a big but: here, the mechanism supports you just enough that missing wrist control or wobble doesn’t ruin your result. Instead, you get, with decent abrasives, blistering sharp edges! If you haven’t tried such a sharpener before – I can only advise you to do that.

The only issue I had while using it is – it feels just slightly too small. You can see me in the video bumping a couple of times into the back of the support – well, I guess I could maybe flip the sled around to get closer? But then I’d probably bump the infinity adjuster into it. On very large knifes, I found that I need to also change the magnet position horizontally, to reach the tip. This could probably be solved by just sourcing slightly longer guide rails yourself – but my one suggestion to the manufacturer would be to make it a bit bigger. Give it some more room to accommodate larger knives.

Conclusion

I mean – from the positive review, you can already see that I am very much a fan from this type of sharpener. Some very positive things stand out here: The device is manufactured by a small, hard working company. The materials are high end, everything is CNC machined and carefully dimensioned. It is super portable, fun to use and gives you fantastic edges. It’s quick to assemble, relatively sturdy and should be very durable.

I think this is pretty much flawlessly executed – good craftsmanship, working principle, fair price, locally made. If only it was 50 mm larger!

Nevertheless, the conclusion to this can only be: get one! I will for sure.

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 has turned into a lesson for me. I read about this stone on the internet, saw a couple of youtube reviews where it gets hyped. According to the manufacturers page, it’s a mixed abrasive stone with a high diamond concentration, some SiC particles in a dense, ceramic matrix. I ordered two different ones – the #400 and the #1000 grit stone. Unfortunately, this stone packs a “surprise” I have been expecting for a long time, but did not expect to meet in this one.

Let’s start with the optical micrographs:

Optical micrographs of the KINTIF #400 mixed abrasive stone. Instrument: Leica Emspira

The stone shows a mix of black and green particles. In the randomly choosen FOV, a large yellow spot is visible. Overall, it looks like mixing could be improved here, but also that a low of abrasive is in this stone.

The #1000 grit stone is lighter in colour, as the smaller particles typically refract the light differently. It is more inhomogeneous as well, with large white spots (probably the ceramic binder?) visible.

Optical micrographs of the KINTIF #1000 mixed abrasive stone. Instrument: Leica Emspira

Let’s start on the SEM pictures! Because the stones are very large, very heavy and porous, but also not very expensive, I chipped off a large piece from the corner – this gives us a nice view inside the composition, and reduced vacuum pumping time. Furthermore, there’s less danger of contaminating the inside of the SEM!

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

We can see two different species of abrasives here – bulky diamonds with a pretty regular size distribution, as well as clear SiC grains that are more irregular, both in shape and size. While zooming in to 1000x magnification, I stumbled across something I didn’t ever want to stumble across. Here it is in very large magnification for you:

The sharpening stone contains nests of thin, sub micrometre fibres with a large aspect ratio. If you look on the 500x or 1000x magnification, more of these can be spotted.

I quickly checked on the #1000 stone: here, we can also find these nests of fibres, with the rest of the morphology similar, just at a smaller scale.

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

Now, why do alarm bells go off in my head when I find fibres in a non-western world sharpening stone? For this, I have to expand a bit. Most abrasives you see on this blog aren’t specifically designed for knife sharpening. They were made to be used in CNC machines, where they rotate at enormous speeds. Some are adapted to better fit the task of hand guided sharpening, but overall: the R&D effort to produce a sharpening stone tailored to hand sharpening is immense, and the market is not.

Now, on rotating abrasives, there are immense centrifugal forces. To give you a sense at what surface speed steel is ground: The general suggested rotational speed is in the magnitude of 35-100 m/s – that’s 360 km/h or 220 mph. Spinning that fast puts enormous forces, especially on large and heavy wheels. Ceramics are not well known to be very strong in the tensile regime. Commercially, large wheels are therefore reinforced, for example via glass fibre or cotton matts. Now, finding chopped, sub micron fibre, let’s a very specific alarm bell go off in my head. You see, I like to collect old books. Specifically, old books about resin technlogy, grinding and abrasives. One of my favourites is the “handbook of plastics – Vol X – Duroplaste”, which came out in 1968, and only exists in German language.

The reason alarm bells go off in my head is, a fantastic fibre reinforcement, that was very popular before we knew what it did is… asbestos. Asbestos really ticks all the boxes in what we want as reinforcement for a grinding wheel: It’s lightweight, good tensile strength, good coating behaviour, heat resistant, cheap, easy to mix and chop to the desired length. Oh, it’s also without doubt super bad for your health as it’s highly carcinogenic.

I’m not a forensic investigator. I know about asbestos, and some basics facts. It’s a fibre, sometimes spikey, sometimes it looks like cooked, limp spaghetti. It’s sub micron, and has large aspect ratios (much longer than the diameter). Let me pull up the picture of that fibre nest again:

Sooooo. Maybe you want to be scared, with me? We can further dig into this, by doing elemental analysis. Asbestos consists out of Mg, Si, O, sometimes with Fe, Ca or Ka. Depending on the mix of these elements, it has different fancy geological names. Let’s take a look at the chemical composition of this fibre nest:

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

Now, is this conclusive? Not really. Because the interaction volume of the electron beam is quite far reaching, and the fibres are thin, and behind it is a ceramic stone that also contains Mg, and O. But if you look at the individual channels, you can make out: no Carbon in the fibres, but the Mg and O channel are very clearly visible in the shape of fibres. This means it’s definitely no organic fibre (like cotton). At this size, any inorganic fibre will be hazardous, quite possibly carcinogenic if it enters your lung. And sharpening creates ultra fine particle dust due to the abrasion.

I am not a forensic expert and have thus far not encountered real asbestos fibre in my SEM life. But this makes me cautious enough, that I won’t be using nor testing this stone, and will dispose of it as special waste. I seldom give hard recommendations in this blog, but with this one, I stand quite firm:

If I was you, I wouldn’t use this stone. And because of it’s origin, I wouldn’t trust any explanation by the manufacturer. Because if this was harmless fibre reinforcement, it should have been part of the marketing pitch – and while I can’t conclusively declare that this is asbestos, I can conclude it’s inorganic fibre and will be bad for your health.

Better be safe and buy a slightly more expensive sharpening stones. There are good alternatives out there.

And on a sidenote: when we zoom out, one can see that there is very little diamond in this stone and mostly SiC – so why not get a nice AO stone like the shapton glass? It’s superb, safe, and a lovely, similar prized alternative.

Second sidenote: I always thought I’d encounter a scary stone one day. I so far thought it would be a historic, soviet era stone or a pre-WW2 german resin stone. Alas – here we are.

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 something REALLY special. They are resin based, CBN sharpening stones from St. Petersburg – made from the special “elbor” type of CBN. Historically, this CBN was characterised by a lower content of CBN, with impurities of hexagonal boron nitride and MgO. Nevertheless, these impurities resulted in blocky shapes with defects such as cavities and inclusions. These increased the surface area, increasing bonding strength to resin, but also self sharpening properties. This is advantageous for their use where low forces and low heat is prevalent – for example, hand sharpening of knives! If you are more interested in reading about elbor CBN – check out this paper:

Volov, V.N., Garshin, A.P. Comparative Indices of Different Grades of Cubic Boron Nitride Abrasive Powders. Refract Ind Ceram 61, 441–450 (2020). https://doi.org/10.1007/s11148-020-00500-5

The CBN stones I have lying here are also true historical ones – as far as I am aware, they were manufactured in 2025, but the CBN powder is from old soviet productions. Truly something special! I was gifted these sharpening stones by Nickolay – thank you very much for your continued support! At this point in time, the manufacturer of these stones does not have a homepage. I will update this review if one becomes available.

The stones are the typical 1×6″, guided sharpening stones style. They came in a nice, printed box and are laser marked to their respective sizes:

Photographs of the sharpening stones from St. Petersburg.

If, like me, you are unable to read Cyrillic font, don’t worry, I got you: The laser marking reads “ELBOR”, the grain size and then in a 2nd line the description “super soft bond”.

Under the optical microscope, more of the bond details are revealed:

Optical micrographs of the 20 µm stone. Instrument: Leica Emspira

We can see a white bond, interspersed with very dark and slightly lighter grey particles. Zooming in, a few bubble spots can be made out, but also that the dark grey spots consist out of agglomerated grains.

Optical micrographs of the 10 µm stone. Instrument: Leica Emspira

This is also visible on the 10 µm stone. I’d guess that this is the same bond, with just a smaller abrasive. The grey spots are smaller, and grains are harder to make out in these.

Optical micrographs of the 5 µm stone. Instrument: Leica Emspira

With decreasing abrasive size, the number of dark grey agglomerated spots increases. This could point towards some trouble with mixing?

Let’s take a closer look under the SEM, to identify what the large black agglomerates are, but also what the bond consists of and looks like:

SEM micrographs of the 20 µm stone. Instrument: Zeiss GeminiSEM 560.

This stone has some topography to it! We can see a number of (probably) CBN particles, fitting the size stated on the stone. The concentration is not super high, but a lot of grains are visible. Interspersed are some voids / bubbles, but also some massively larger particles. The bond itself seems to be very fine and regular, with some tiny filler particle in it. The CBN grains themselves definitely look like Elbor grade -they are irregular shaped, having a sharp appearance.

SEM micrographs of the 10 µm stone. Instrument: Zeiss GeminiSEM 560.

The 10 micron stone looks very similar – but also, the larger filler particles in this stone are easier to make out! The concentration is similar to the 20 µm stone.

SEM micrographs of the 5 µm stone. Instrument: Zeiss GeminiSEM 560.

For the 5 µm stone, we have a lot of pictures to dig thorugh. In the overview, we can see that this stone also has large filler particles that most likely aren’t CBN, as they are flat ground. But there’s also one of the spots of agglomeration we were able to make out in the optical microscope here! Zooming in on that one, we can see that it contains a lot of loosely held abrasive particles. This is a clear case of agglomeration. It is only natural that on the finest stone, this is the most visible, as it’s more difficult to properly mix fine powders.

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

We can see the distribution of the CBN particles (N, B) all over the FOV. Moreover, we can see that the resin bond is heavily reinforced through ceramic filler particles. Most noteably, oxide ceramics build from Al, Mg and Ca.

EDS analysis of the stone 10 µm stone. Instrument: Oxford Ultim Max  ∞ 40mm² EDS sensor. Note that our EDS sensor doesn’t show elements lighter than boron.

The same bond is visible on the 10 micrometre stone. Here, we can also make out one of the large “super particles” we spied in the SEM overview. It looks like alumina oxide.

EDS analysis of the stone 5 µm stone. Instrument: Oxford Ultim Max  ∞ 40mm² EDS sensor. Note that our EDS sensor doesn’t show elements lighter than boron.

This continues on the 5 µm stone – same bond, ceramic reinforced resin bond. But here, we can also make out the agglomerated part on the far right corner of the FOV. Let’s focus a bit more on this one:

The particle agglomeration is mostly CBN – the fine particles clumped together, and during dressing they formed a small void, as only the ones with contact to the resin bond remained behind. The red particles around it are CaO.

Now from morphology and elemental analysis, I did not expect a good performance from this stone. Previously in this blog, all stones that showed massive amounts of agglomeration and larger fill particles behaved badly during the sharpening action. But this is why I always sharpen a bit with the stones and prepare a blade edge!

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. These stones were tested in NitroV at 60 HRC. I’ll supply M398 pictures at a later date, but our small SEM is currently broken – bear with me for a couple of weeks! For now, enjoy HD pictures form the big SEM.

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

SEM micrographs of the edge finished with the 20 µm stone in NitroV. Instrument: Thermo Fischer PhenomXL SEM.

The 20 µm stone leaves a very regular appearance on bevel. Some deeper scratches are visible from time to time. The cutting edge has a large, foil type burr that is quite ragged. This slices easily into a piece of paper!

SEM micrographs of the edge finished with the 10 µm stone in NitroV. Instrument: Thermo Fischer PhenomXL SEM.

The 10 µm stone further refines this edge. The overall surface morphology improves, becoming smoother, but some larger scratches come through, still. This is most likely the super large aluminium oxide particles we have seen in the SEM. The cutting edge shows less burr, and some ragged parts remain. The blade was quite sharp at this point!

SEM micrographs of the edge finished with the 5 µm stone in NitroV. Instrument: Thermo Fischer PhenomXL SEM.

Lastly, the 5 µm stone further refined the surface. We have a micrometric foil type burr remaining, some deeper scratches and clear prow/burr formation visible in the surface morphology. The chamfer itself is shiny, but not glossy. The apex is not super fine – I think this stone exhibited quite a bit of pressure from the ceramic fillers, breaking off the burr and leaving a wider-than-necessary apex. It is in my personal opinion the weakest stone out of this set – I’d guess that going to 10 µm and then stropping would leave you with the best and well formed edge.

So, a final and very subjective conclusion: the stones themselves are wonderful. Nice feedback, quick acting, low tendency to load and give a sharp edge with a very regular, homogeneous grinding pattern. They do burnish a bit and cut less clean than a pure CBN or diamond stone does, which leaves one with a larger burr than one would expect. The sometimes very large oxide ceramic particles, but also heavy agglomeration on the smaller sized probably reduce the performance. Nevertheless, this stone set is high performance and because of the historical CBN powder something very special – they will remain in my collection as a cherished set and will be used from time to time.

I have zero ideas how one would go about buying these – my understand is they are made to order and probably impossible to get in the western world. If you do have a chance to snag a set – I’d go for it.