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!