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 japanese artificial sharpening stone. The Imanishi “Bester” series is supposed to be usable after just splashing with water, instead of soaking. I think this sounds very promising for a guided system! Funnily enough, in my native German language, “Bester” means…the best. Let’s see whether this is true:

Optical micrographs of the stone. Instrument: Leica Emspira

The stone is an off-yellow-whiteish colour. Some darker particles can be identified all over the stone, some black, some just off colour.

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

Under the SEM, this stone shows a mix between blocky, fine particles and some smoothed over plateaus. In these plateaus, fine abrasive dust fills the voids, making it appear denser. Overall, the grains are either very blocky, or very flakey!

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.

This stone shows a wonderful colourmap of the elements! This is once again a mix between SiO2 and Al2O3, but wonderful homogenous in it’s distribution! It appears as if they have the mixing down. Some foreign particles, especially of K, Ca can be detected. This is to be expected in oxide ceramics, and their percentage is very low (< 1 %).

3D surface height map of the stone. Instrument: Bruker Alicona µCMM, 50X objective lens, 3×3 FOV high resolution focus variation scan. Data is leveled and outliers removed (0.25%).

The 3D height map shows a smoother surface, with lot’s of plateaus and very little voids. This makes this stone exceptionally smooth for an oxide stone, the Sa and Sq values reflect this.

ISO 25178 parameters.

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.

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 edge made by this stone is quite sharp – it BESS tested at 110! Moreover, the stone had a very nice, smooth friction based feedback and quickly build up some abrasive slurry. The whole surface was matted more or less instantly – it doesn’t really hit my aesthetic, but is remarkable nevertheless. This matte surface stems from thousands of micro scratches all over the surface. To show this, I’ve taken a picture in the middle of the cutting edge surface:

Overall, this stone made a very homogeneous, sharp edge. It is well manufactured. I don’t think it’s the correct choice for such a high carbide steel, and would probably perform better on a high carbon steel. I hesitate to state this…but I kind of liked this stone!

Sharpening disclaimer: I use a standardised approach to sharpening, which basically follows how most manufacturer of guided systems tell you to use this system. I am very aware, that every stone could perform much better than this, in terms of sharpness, but I want a comparable approach. The sharpening segment mostly shows the material removal mechanism – is it burnishing? is it cutting? is the cutting pressure too high so that carbides crack? Is there massive burr or prow formation? The BESS value definitely doesn’t highlight the ultimate sharpening performance of the stone, but was an often requested information. Over time, this blog will show BESS values for different edge morphologies, but by the holy endmill – don’t read it as a „this is the max value this stone can achieve“. I would also suggest to familiarise yourself with the works of Immanuel Kant, it’s absurd I need to write such a disclaimer here.