TL;DR: Dr. Marv takes a look at the first stone of the “coarse” grit set. It’s his own design, super high performing sharpening stones. Come along to see the composition in the SEM, and compare SEM micrographs of the blade bevel.

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Review

Today’s sharpening stone is something very, very special. I humbly and very proudly present to you the result of spending a decade in the pursuit of REMOVING MATERIAL. The mad Dr. Marv bring’s you the fabulous:

Dr. Marv’s Scientific Sharpening Stones – Coarse Grit Set

This is my own design. I offer these stones in 3 sets – Medium (20 µm, 10 µm, 5 µm), Fine (2.5 µm, 1 µm, 0.5 µm) and now in a Coarse set (80 µm, 60 µm, 40 µm).

The coarse set features a different bond then on the medium and fine set. It is based on the same, scientific principles: rigorous testing, evolution and quality control. At the same time, I felt that a set that is used for re-profiling or setting an edge should be a bit harder. I changed the formulation of the bond and also developed a thermal tempering process that increases the hardness of these. It’s an additional manufacturing step, but oh so worth it. They are noticeably harder than the medium and fine grit set, and the concentration of diamond by weight is even higher.

(Note: the fine and medium set will remain on their high performance bond which is a bit softer than this one)

Optical micrographs of the 80 µm stone. Instrument: Leica Emspira

The stone is a slightly greenish colour, which stems from the diamond type used. We can see regular stripes going from left to right, with a low roughness. All particles are either sparkling diamond, or if oriented in a way that no refraction happens, pure greenish diamonds. The bond itself is colourless and off white. The diamonds are really large and easy to make out – this is a real 80 µm resin stone!

The stripes that can be seen are the result of the dressing employed. If you’ve read my article on dressing, or any other review, you’ve realised by now that flattening/dressing is a source of contamination. In order to avoid this, I use single point diamond chiseling – a very advanced manufacturing technique, where a very sharp, lapped diamond tool is moved in a linear motion across the surface. This has the advantage, that no foreign particles can be pushed into the surface, and exceptionally smooth and flat surfaces can be created. Compared to the medium grit set, I use a finer stepover on these stones. (okay, the medium stones are now also chiseled finer…).

In order to better show the diamond density and distribution, I took a stone and broke it in half. What you are looking at above is the “cleaved” surface through the stone. We can see that a) this is only and purely diamond! no foreign particles! and b) there is a MASSIVE amount of diamond in this stone. Compare this to any other diamond stone you have seen before on this blog.

SEM micrographs of a broken through stone. Instrument: Zeiss GeminiSEM560

The concentration visible is much higher than on similar grit stones we have had on this blog. It’s really hard to make out the resin between the individual grains – I don’t think a higher concentration has ever been achieved!

Because of my proprietary treatment of the diamond, fantastic grain retention is achieved. It is specifically adjusted for the new resin to allow for some self sharpening, but remain a solid, long lasting stone.

SEM micrograph of the used diamond powder. Instrument: Zeiss GeminiSEM560

This first batch has the following particle metrics:

Particle metrics for the 80 µm nominal sized 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. For this blade, the edge was first set with a coarse F150 electroplated diamond stone, and then prepared with the Dr. Marv 80 µm sharpening stone:

SEM micrographs of the edge after preparation with Dr. Marv’s 80 µm stone. Instrument: Thermo Fischer PhenomXL SEM.

Looking at this picture, we can see that the stone is leaving us with a wonderful, homogenous and smooth surface already! There are no deep scratches, and the bevel surface is really shiny already. Moreover, the apex is nicely refined and fine – but a bit serated. I think this set will really be for those sharpeners, who prefer a toothy edge. But also, those that want a flawless finish. I found that on smaller grits, I had to spend way less time to get rid of the deep scratches typically apparent from setting the bevel via EP stones.

If we zoom in even more, we can make out a fascinating detail:

SEM micrographs of the edge after preparation with Dr. Marv’s 80 µm stone. Instrument: Thermo Fischer PhenomXL SEM.

The debris you see very close to the cutting edge is actually the “chips” and shavings that are created by the stone. Because of the uncountable number of diamond cutting edges, this stone is cutting miniscule small chips. This helps with slower loading, but also provides that super smooth surface. It’s also a wonderful proof that this stone is actually cutting, and not burnishing. The fine and even distribution of chip size also highlights the tight particle control – there are no foreign, larger particles in this stone.

Edge prepared with the 80 µm Dr. Marv stone. The surface is super smooth and homogenous!

This is also reflected in the optical micrographs under our Leica Emspira microscope: A very glossy, shiny surface, with a toothy edge. I think some people, especially for rugged outdoor knives are going to be over the moon with this set!

That’s it folks. I’m very proud to announce that these are now available in a very limited handmade batch. Link is here or find it in the shop the top of the blog!

The coarse grit set of Dr. Marv’s Scientific Sharpening Stones in their storage box. Proudly handmade by Dr. Marv in the German Alps.