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

Today’s sharpening stone is another Jende resin stone. We’ve had it’s larger brother, the 120 µm on this blog before – check it out here.

This episode, we’ll dig into the 30 µm stone. It’s a light colour, showing a mixed-abrasive appearance to the naked eye.

Let’s take a look under the optical microscope!

Optical micrographs of the Jende 30 µm resin stone. Instrument: Marvscope

The stone itself shows quite the irregular composition – there’s areas that are more yellow-ish in colour, some very white spots, but also black particles interspersed. Moreover, even before use, the stone feels very friable – rubbing your finger along it, it has a lot of feedback and bite, but just doesn’t feel fully solid.

Let’s take a closer look in the SEM:

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

The stone has a lot of abrasives grains in it – there’s certainly some diamond, but also some oxide particles in different sizes visible. The diamond particles don’t really look very homogeneous in size – I’d postulate from the pictures that this stone exhibits a quite large spread in particle size.

Some grains show clear delamination from the binder already – very curios! Remember, this is always before actually using the stone.

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 Jende 30 µm resin stone. Instrument: Oxford Ultim Max  ∞ 40mm² EDS sensor. Note that our EDS sensor doesn’t show elements lighter than boron.

The stone itself is a mix between diamond particles – the feeling that the size differs wildly is confirmed here. Particles approach nearly 50 microns at the upper end, but there is also diamond particles in the sub 10 micrometre size. The distribution of the diamond is less well done than on the 120 µm stone, too. Moreover, the stone has large and small ceramic particles in it, of different species. There is some Mg-Si-O, but also some pure Al2O3 particles. Again, there’s quite a bit of sodium particles – very curious! The stone overall is a colourful one, with lots of different elements in it. Pretty!

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. Afterwards, the tested stone is used, first in a back and forth movement until the surface becomes homogenous, and then alternating strokes (5-5-3-2) on each side, for a total of 20 strokes towards the apex per side. No pressure is applied but the weight of the apparatus. Moreover, the same approach is repeated with a blade in NitroV.

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

The stone itself exhibits an exorbitant amount of feedback – but is super friable. Even after just a couple of strokes, it starts to form a slurry of abrasive particles on the blade. This slurry of course boosts material removal rate -but the rolling abrasive grains also mar the surface. Moreover, when wiping off the residue, there’s a high chance to scratch the blade, and if one doesn’t clean it properly, there’s certainly the chance to contaminate subsequent sharpening stones with the residue particles.

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

SEM micrographs of the M398 edge finished with the Jende 30 µm resin stone. Instrument: Zeiss GeminiSEM 560

The surface shows clear signs of that friable stone nature – the surface morphology is dominated by pitting, burrs and prows on the bevel. Moreover, the apex is not really refined nor much finer than on the 120 µm stone. A large number of black particles embedded into the blade can also be made out – these are typically in the sub 5 µm range.

This translates into a very matte look for the bevel, and a toothy edge:

Optical micrograph of the M398 bevel. Instrument: Marvscope

Which is further visible in the white light interferometer measurements of the bevel: a diffuse, marred surface:

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.

On popular demands (thanks to Branislav for requesting this!) I’ll include surface roughness parameters for the bevels:

Sa	0.3792	µm
Sq	0.5065	µm
Ssk	-0.7194	–
Sku	4.913	–

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 softer steel shows even more signs of plastic deformation through large rolling grains. There’s also deeper scratches, as the softer matrix doesn’t resist the larger ceramic oxide particles as well as the M398 steel does.

A much higher number of black particles made me curious – so I bumbed the voltage of the SEM and did another SEM analysis, this time focused on one of these particles.

The curious black particles we find embedded into the blade are pieces of diamond, that because of the friable nature of the sharpening stone are rolling around, and then embedding into the blade:

EDS analysis of a particle embedded into the blade. Instrument: Oxford Ultim Max  ∞ 40mm² EDS sensor. Note that our EDS sensor doesn’t show elements lighter than boron.

The surface sometimes also shows much deeper scratches – I would imagine this comes from a > 30 µm particle becoming loose and dragging through the surface before going over the edge and accumulating on the second side of the bevel.

Optical micrograph of the NitroV bevel. Instrument: Marvscope

WLI confirms the existence of deeper scratches on this bevel:

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.

With the surface parameters also taking a small dip and being slightly coarser/rougher:

Sa	0.4167	µm
Sq	0.5606	µm
Ssk	-0.9312	–
Sku	5.064	–

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

Overall, this is a quick acting stone. If you have tried adding abrasive paste (for example CBN paste) to a stone before, you have experienced that loose abrasive really boosts material removal rate. At the same time, at 30 micrometre, properties I look for edge refinement, removal of scratches and general increases in sharpness. Because of the highly friable nature of this stone, bad grain adhesion, insufficient mixing, mediocre particle size control and large ceramic oxide particles in it, the performance of this stone is overall very mediocre.

I think at this price point, there are plenty of higher performing alternatives out there. A pity, because the feedback for sure is nice!