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