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 for my own product, so therefore it could be considered an advertisement in certain countries. You are hereby warned.

Review

Today’s sharpening stone is the 2nd member of my “experimental series”. Reading my blog, you might have discovered: This young *coughs* Doctor loves diamonds. They are sparkly and shiny and my favourite abrasive. Nevertheless, I’m a naturally curious person. Many abrasives are used to shape metal – some more on the soft side, some are added as filler to the stones we all use.

In my “experimental series”, I explore the concept of different abrasives in their pure form. You could consider my Scientific Sharpening Stones the “diamond version”, and last year I published (and released a very limited edition!) of the experimental series in CBN. They are called “experimental series” for a reason – I do not think that these stones will outperform my Scientific Sharpening Stones. I actually would be surprised if they have a higher performance. But I am unable to test them in every condition, every steel and also – sharpening is a very subjective thing. Maybe some people will love the edge produced by this. I think some of my avid readers might be interested in trying this out – and become the scientist themselves through their experiment! 

Today I’m introducing my SiC experimental series – and I can already tell you: surprisingly enough, I absolutely love them.

SiC is an interesting abrasive – I’ve written about it before in my “abrasive snippets” section. It’s quite hard at around 2800 HV (CBN: 4500-5000 HV, Diamond: 10000 HV, most steels: 800-1000 HV), very inert, temperature stable and wonderfully bonds to resin.

SiC exists in many different structures, which are called polytypes. For these stones, I’ve used the harder type, 6H – SiC, which is black. It’s more brittle than it’s green cousin.

The stones I made are 30, 15 and 5 µm size, and have a wonderful, black-greyish colour:

A picture of the very first “SiC Experimental Series” Stones.

Let’s take a look under the SEM – stone by stone. For this, I’ve broken a stone in half to enable us to look at the cross section:

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

Something that immediately stands out is not only the high concentration – but also the success in distributing the grain: SiC often clumps together in commercial sharpening stones, but here we have a fantastic mix and wonderful distribution over the whole Image!

To test it’s performance,, a blade was sharpened with my typical approach, read about it here. As this is a relatively soft abrasive, I’ve sharpened a blade in NitroV at around 60 HRC. While the stones do remove material (I’ve tried it with good success in Magnacut and M390, and with very little success but some material removal in M398 at 65 HRC), this is an abrasive best suited for old fashioned, lower carbide content steels.

SEM micrographs of the edge finished with the 30 µm SiC stone. Instrument: Thermo Fischer PhenomXL SEM.

The 30 µm stone is a beast. It actually abrades material quite quickly, after just a few strokes there’s a lot of chips swimming in the thin coating of oil on the blade. The apex itself looks pretty toothy, but also quite refined. I’m really surprised here – but this is actually very decent, considering it’s no superabrasive!

Next, let’s take a look at the 15 µm stone:

SEM micrographs of the 15 µm stone. Instrument: Zeiss GeminiSEM 560.

Once again, a wonderful distribution and quite high concentration. I’ve continued sharpening the NitroV – but want to share picture from the sharpening progression here:

Swarf and chips on the blade after sharpening for about 30 seconds with the 15 µm stone!

Do you see the amount of swarf, swimming in the oil? These stones definitely cut! Let’s take a look at the apex:

SEM micrographs of the edge finished with the 15 µm SiC stone. Instrument: Thermo Fischer PhenomXL SEM.

This was already a really sharp blade. Sharp enough, that it easily sliced into a tissue. We see both a refinement on the surface, but also the apex.

Last but not least, we need to take a look at the 5 µm stone:

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

This stone seems to have an even higher concentration – but as I do my stones in “weight” and not some obscure, hard to verify volume concentration, it’s exactly as much abrasive as on the previous stones. But: With the smaller grain, this means a much higher count of potential cutting edges. The blade was then further sharpened with the stone:

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

This is actually a pretty decent apex. It’s thin, pretty regular at normal magnifications. Only at 1000x, the toothy and waviness really becomes visible. Some part of the edge has been slightly folded over in a foil type burr, which wasn’t really visible with the 15 µm stone. The surface finish of the bevel is further refined, but still shows a plethora of scratches.

The stones themselves are pleasant to use. They have a bit more feedback, which probably stems from all the sharp, pointy SiC grains. If you’ve read my review about my experimental series in CBN, you probably got the message that I was a bit disappointed – they were good stones, but fell shy of my diamond stones. I’m not saying that these SiC stones perform better. They definitely don’t. But they are fun to use, and they give a blistering edge – and most of all, the surface finish left on the bevel is very special. Instead of a perfect polish, the surface is marred by thousands of fine scratches, giving a shiny, matte appearance, that changes colour in thousands of rainbows when you twist and tilt it in the light:

The appearance of the edge under a Leica DMS 300 microscope. The light source is moved back and forth along the apex.

Honestly, this is not my highest performing stone. The CBN stones are objectively better at slicing through high tech steels. But: they are fun to use, if the steel they are used on is a good fit. They have a pleasant feedback. The bevel created is wonderful – it’s exciting, ever changing and has some character that a perfect mirror never could have. I honestly love these stones. My good friend Roman Kasé, when I told him about this experience didn’t stop laughing and told me “welcome to the oldschool feedback gang!”. Not sure I am there yet, but these stones WILL get used again and again.

Dr. Marv’s Experimental Series in SiC is available now, in a very limited, individually numbered edition of 10 sets.