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 TSPROF Alpha – but this time a very fine one, with 5 µm diamond grain size! Do check out the previous review under this link.

Optical micrographs of the TSPROF Alpha 5 µm stone. Instrument: Leica Emspira

The finish of this stone is comparable to the 120 µm one. It does not contain any overly large particles. Nevertheless, some black and white spots can just barely be made out under the microscope. Let’s take a look under the SEM!

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

The SEM pictures show a similar appearance of the binder than on the 120 µm one. It’s a bit flakey, and quite uneven. There are several particles of a different colour and size than the dark grey diamond grains. To highlight this difference, I’ve taken some BSD pictures, that show elemental contrast:

Back Scatter Detector SEM micrographs of the TSPROF Alpha 5 µm stone. Instrument: Zeiss GeminiSEM 560.

Here, lighter elements appear darker than heavier elements. So all the bright particles you can see above are actually not carbon based, but consist out of heavier elements – something I wouldn’t expect in a “pure” diamond resin stone. I suspect we have some fillers, but also abrasive particles from the factory dressing in here.

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 TSPROF Alpha 5 µm stone. Instrument: Oxford Ultim Max  ∞ 40mm² EDS sensor. Note that our EDS sensor doesn’t show elements lighter than boron.

The EDS analysis shows some Silicon carbide particles, some Aluminium oxide, and a low concentration of agglomerated diamond.

EDS analysis of the large particle in the TSPROF Alpha 5 µm stone. Instrument: Oxford Ultim Max  ∞ 40mm² EDS sensor. Note that our EDS sensor doesn’t show elements lighter than boron.

Let’s take a look at the surface morphology under a 3D measurement microscope!

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%).

This stone is much flatter and smoother than the coarse stone, and the ISO 25178 parameters 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 stone had a smooth feedback during sharpening. The surface quality visibly deteriorated from the preparation with Dr. Marv’s Scientific sharpening stones. In the SEM micrographs, we can see a couple deeper scratches, which translated to a slightly matte surface. The apex is nicely formed and very thin. This is a stone that can make sharp edges! If only the finish was a bit better.