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

Todays sharpening stone is something I have been looking forward to since I heard the announcement – and immediately ordered one. It’s the first stone from fellow sharpener and youtuber “Edge Works Knife Studio”. According to him, the stone is a zero compromise, finely tuned resin stone, which delivers the results and feedback he has been looking for in a stone. He sells them for a very affordable price from the US, and was an absolute pleasure to do business with – clear communication, proactive emails and in my case also a very friendly solution to shipping his stone overseas. I think this is the definition of someone starting a small business and doing very, very, very well in it, which is why I mention it.

Today’s stone is the #1000 grit, which is “the one stone to buy” (heavily paraphrased). It’s a resin bonded stone – on popular demand here are 2 photos of it:

Photos of the EdgeWorks Resin bonded diamond stone “as delivered”. The base looks to me like media blasted aluminium. The resin layer is bonded to it via some intersecting elements. The stone is a light green colour.

Let’s take a look under the optical microscope!

Optical micrographs of the stone. Instrument: Marvscope

The green colour is confirmed further in the optical microscope. We can make out some clustering of particles – some of a very dark, grey colour, some of a deeper green then the surrounding matrix.

Let’s take a closer look in the SEM:

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

The stone shows a typical, slightly friable resin bond. There is a plethora of different abrasive grains inside it – some very small ones, but also some larger and a lot of medium sized grains. The very largest grains do show a standard diamond morphology, whereas the medium sized ones are closer to silicon based abrasive grains.

Chamberscope view of the stone inside the SEM.

Something I often check with stones, but mostly with natural stones is whether they show any cathodoluminescence – most don’t, but this one does:

VPSE Sensor image of the stone with 0V bias – showing slight catholuminescence. Cool!

Is it important? No. Is it very cool that some parts of the stone emit light when hit with high energy electrons? Heck yeah.

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 resin stone. Instrument: Oxford Ultim Max  ∞ 40mm² EDS sensor. Note that our EDS sensor doesn’t show elements lighter than boron.

The stone shows a relatively typical composition for a chinese resin stone. We can see some diamond, but also lots of “secondary abrasives”, that are supposed to make the bond firmer. In hand sharpening, these Si, Al and Mg based oxide and carbide ceramics add a lot of feedback – the blissful, constant vibration you experience is caused by these grains. Moreover, this stone contains a surprising amount of titanium – probably mostly in the form of titaniumoxide, which is often found with the other oxide ceramics. There is quite a bit of chromiumoxide, too – which explains the green colour of the stone.

Zooming in a bit closer, the EDS highlights some issues with the mixing of htis stone – the diamonds tend to agglomerate a little bit. This likely will result in larger-than expected scratches and maybe even some raggedness to the cutting edge.

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. As this is a Benchstone, I sharpen using a Katocut Nowi Pro, so that the angle is kept constant and my skill is not the defining characteristic in the result. Afterwards, the tested stone is used. No pressure is applied but the weight of the blade. Moreover, the same approach is repeated with a blade in NitroV at 59-60 HRC.

The edge is then analysed in the electron microscope for breakouts and morphological appearance.

Let’s start with the harder steel – the M398 blade:

SEM micrographs of the M398 edge finished with the resin stone. Instrument: Zeiss GeminiSEM 560

The stone seems to struggle a little bit with the high carbide content M398 – we can see that the apex is deformed and folded towards us. This would feel to the “thumb test” like an easily detectable burr – but actually is more akin to some damage to the apex. I applied very little pressure on the finishing passes – the weight compensation of the Katocut was adjusted accordingly. The bevel itself is quite smooth – surprisingly so for a #1000 grit stone. Magnifying a bit further, we can see some slightly deeper scratches – but also that the whole surface gives a plastic-deformed look, with lots of prows and micro burrs formed near the trails of the abrasive. This is a clear sign of a dominant burnishing action – which typically gives a nicer, glossier finish, but less of a well refined apex.

Close up SEM micrograph of the M398 bevel. Note the burr and prow formation near the tracks of the abrasive. Ignore the dirt on it. Instrument: Zeiss GeminiSEM 560.

Optical micrograph of the M398 bevel. Instrument: Marvscope

This is visible in both the optical micrograph, but also the 3D surface scan. The slightly folded over cutting edge is visible:

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.

With the surface roughness parameters being very low – as expected after seeing the burnishing effect.

Sa	0.0639	µm
Sq	0.1081	µm
Ssk	7.114	–
Sku	278.8	–

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 NitroV edge looks much cleaner. This steel is not only much softer, but also has less of a carbide content. The stone seemed to have an easier time with this one – proper cutting and a refined apex was achieved.

Optical micrograph of the NitroV bevel. Instrument: Marvscope

The surface morpholgy reflects this in the optical micrograph, albeit some “toothiness” to the edge is visible. This is something most kitchen knives sharpener are looking for – and this also seems a major point for what this stone was developed.

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.

The surface roughness is slightly higher than on the M398 bevel – which was expected, seeing how the stone exhibited less burnishing and more clear cut tracks.

Sa	0.08539	µm
Sq	0.1120	µm
Ssk	-0.2279	–
Sku	4.489	–

ISO 25178 surface roughness parameters. S-Filter: 2.5 µm (gaussian), L Filter: 0.25 mm (gaussian). No F operation besides LSQ leveling.

The stone itself has a smooth, but noticeable feedback. It is immediately obvious, that someone who is a skilled manual sharpener and cares a lot about “feedback” helped adjust the formulation of this stone. If you are into kitchen knives, and freehanding, I think this stone is a very good choice. Pleasant to use, quite fast cutting, good working edge and a very fair price (at the time of this review, about 120$). I feel like it could be improved by more care in the manufacturing process – a bit better mixing, increased diamond concentration to perform better in “super steels”, while hopefully not loosing out to much of it’s feedback for freehand sharpening.

It’s a good stone for kitchen knives, and a nice project from someone who cares deeply about sharpening and the knife community. I think you could do a lot worse, and in this price range there are not a lot of options where you could do better. My biggest issue with this stone is – they are not made in America. Which is a given at this price tag, but for me, who cares deeply about manufacturing in the western world, it pains me a bit.