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 a japanese whetstone – the Shapton Pro Ha-Nu-Korumaku at 1000 grit. It’s a coloured alumina oxide stone. Shapton has a stellar reputation in the sharpening world. The 1×6″ version I bought was purchased through a German online shop.

Let’s take a look under the optical microscope:

Optical micrographs of the stone. Instrument: Leica Emspira

We can see some larger, very white particles in an orange matrix. The white particles are most likely the aluminium oxide – the purer, the whiter it becomes!

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

I’m not sure about you, but I am not surprised at this point! It’s exactly what one would expect: AO particles of the correct size in a hard, brittle matrix. This is not surprising, as it’s a japanese stone and they have a reputation for honesty and hihg quality products. I’m curious though, what the chemical composition is like!

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

The EDS analysis shows it’s a mix between different oxides – mostly Al2O3, MgO and to some lesser extend CaCO3 and SiO2. It’s quite tricky to make any oxide ceramic ultra pure, and probably also not needed for this stone. I think it’s therefore save to declare that it’s Al2O3 particles as the main abrasive, in a matrix of other, softer oxides that make up the bond design.

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. As this is a water stone, I’ve used water instead of the typical oil.

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

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

The stone struggled quite a bit with the M398 steel I use for the tests. The apex was rounded over a little bit, and overall during use, it felt like the stone looses more than the steel edge I’m trying to sharpen. Moreover, some larger particles introduced pronounced scratches. Overall, I think the blade got noticeable duller due to the preparation with this stone. But from it’s composition, general well made quality, I would guess that this is an exceptional (and very affordable!) stone for less high-tech steels.