TL;DR: Dr. Marv takes a look at the first stone of the “fine” 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. When you are ready, step up your sharpening game. Or don’t, this blog will continue no matter what! 🙂

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. Note: this review is for my own product and in certain countries can be considered as advertisement. Therefore: beware, WERBUNG!

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 – Fine Grit Version

This is my own design. I’ve written a bit more about this on the 20 µm stone review. Check it out here. I’ve also written about the 10 µm stone, check it out here. And I’ve written about the 5 µm stone, check it out here.

After the first couple dozen sets arrived at customers, and feedback was enormously well – it was clearly time to get started on the next set of stones. After all, we are forever in the pursuit of a SHARP apex. And of course, that elusive sub-nanometre mirror finish!

Today we’re going to look at the first stone of the “fine” grit set. It’s the 2.5 µm nominal size Dr. Marv stone:

Optical micrographs of the 2.5 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 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

As a side note and from a professional microscopy point of view – this is super tricky to visualise! The diamond is non conductive, the resin is non conductive, and we have to get REALLY close to see something. If you look at the pictures, you can see that we still have quite a bit of charge up artefacts (the “clouds” forming), even though our beam current is only 5 pA. That’s pico, as in 10 to the power of -12. To give you some sense of how much this is – a µA is 10-6 A, and the typical “leakage current” in electrical circuits. At pA, we are talking about thousands of electrons per millisecond. That’s so little “brightness” for our picture, it’s absurd we actually get a picture. Sheeesh, I love this SEM. Thanks Zeiss <3

Let’s take a step back from cool microscopy facts and note one thing: the concentration visible is much higher than on similar grit stones we have had on this blog. Moreover, the diamond is actually pretty nicely dispersed – this shows that we have no agglomeration here. I think this might be one of the rare few commercially available stones, maybe the only one with this grit that do not show agglomeration and have a density that actually removes material!

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

This first batch has the following particle metrics:

Particle metrics for the 2.5 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 a F400 and F600 EP diamond stone from TSPROF. Afterwards, it is ground with Dr. Marv’s 20 µm stone. Then the Dr. Marv’s 10 µm stone. Followed by the Dr. Marv’s 5 µm stone. To refresh your memory, this was our cutting edge afterwards:

SEM micrographs of the edge after preparation with Dr. Marv’s 5 µm stone. Instrument: Thermo Fischer PhenomXL SEM.

Let’s compare this with the edge from the 2.5 µm Dr. Marv stone:

The edge has become finer – surface details are no longer possible to make out with our desktop SEM. This means our surface is now better than a roughly 150K microscope can resolve! That is enormous. The apex is more delicate, and also more homogenous. Seriously: this is one fantastic edge! Without stropping, I achieved a BESS score of 83. I am quite sure this is not the limit on this.

Moreover, the surface finish of the apex has improved by leaps and bounds! Take a look at this lovely reflection:

In order to further highlight the progression, here’s SEM pictures of the cutting edge at every preparation step:

SEM micrographs of the edge at different preparation steps. From left/ first picture onwards: EP F600, Dr. Marv’s 20 µm, Dr. Marv’s 10 µm, Dr. Marv’s 5 µm, Dr. Marv’s 2.5 µm. Instrument: Thermo Fischer PhenomXL

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!

Reviews of the 1 µm and the very experimental 0.5 µm will come at a later date. While I consider the 2.5 µm stone to be EXCEPTIONAL in every regard, the 1 µm and 0.5 µm challenge my skills – I’m not yet at a proficiency where I can post a review and do these stones justice!

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