Counting scratches: abrasion by the Wicked Edge pastes

In my experiments with the Wicked Edge stropping pastes I had seen that they were very effective in smoothing scratches by means of burnishing. The 10 and 14 micron pastes could not completely wipe out the scratches made by the 1000 grit stones, but they could make these scratches considerably less wide and deep. And the 5 micron and 14 micron pastes were amazingly effective after the 1600 grit stones, creating a very smooth surface.

A question that remained was where the pastes would fit in in a progression of stones/strops based on the amount of abrasion they cause. We have already seen that the 14 micron paste works fine after the 1600 grit stones (2.85 microns) and doesn’t ruin the edge. However, the paste is abrasive, does cause scratches and at some point it will not improve the edge anymore. I wanted to know where that point was: what is the width of the scratches made by the Wicked Edge diamond pastes?

An error-prone, subjective and speculative method

The only method I could think of (given the limitations of my equipment) was to count the number of scratches on an area of a certain width. And then divide the width of this area by the number of scratches.

This method is prone to error, subjective and speculative.

Why is this error-prone? Well, a rather important question comes up: what is a scratch? One might ask this question in a philosophical context, but in my experiments this question posed itself in a more practical way. The scratches are small. Very small. And the lighting of the images is sometimes such that scratches are hard to see.

Counting scratches is subjective as well. The smallest spot my microscope can detect is slightly over 1 micron x 1 micron. Fortunately we are not looking at small spots, but at tiny scratches which usually have a similar size and are quite evenly spaced. And fortunately the human eye and brain are very good at distinguishing patterns, both the collection of dots that together represent a scratch, as well as the collection of evenly spaced scratches produced by a stone or strop. So in practice we can see scratches even smaller than 1 micron. However, since this pattern recognition requires interpretation of an image by the brain, it is subjective. Your mileage may differ from mine.

And counting scratches is speculative. One obtains results from an already error-prone and subjective process and then has to interpret them. But what does it say if the scratches are, say, 2 micron wide? That the pastes contain 2 micron particles? No. We have already seen that the Wicked Edge 14 micron paste does not leave 14 micron wide scratches and that the Dovo green paste does not leave 6 micron wide scratches. Even a 1000 grit diamond stone (7 micron according to the grits comparison chart) probably does not leave 7 micron scratches, since that would require the entire width of the diamond to make contact with the edge. Are the scratches that seem 2 micron wide also 2 micron deep? I have no idea, that depends on the shape of the particles.

Moreover, what does it mean if the counting process leads to the conclusion that the scratches are 2 micron wide? Can we then conclude that the scratches are 2 micron wide? No, because errors and subjectivity contributed to this result. If you want a hundred percent certainty, you cannot conclude anything.

However, I think that if the counting process leads to the conclusion that the scratches are 2 micron wide, it is very likely that the scratches are not 20 micron wide. It is also very likely that they are not 0.2 micron wide. In other words: I think the counting process can tell us what the order of magnitude of the width of the scratches is.

The method

I first tried to find the best pictures of edges stropped with the Wicked Edge diamond pastes on the Internet. These appeared to be pictures that Clay had posted in a threat on the Wicked Edge forum.

I opened these pictures in Photoshop and rotated them such that the scratches were vertical. I then cut out an area of the picture that represented 0.01 inch, or 25.4 micron, of the edge. I blew up the pictures until I could see the scratches most clearly (usually 5x or 6x magnification). This took some Zen and tricks like looking through the eyelashes or moving closer to or further away from the monitor.

I then counted the number of scratches on this 0.01 inch wide edge. A scratch can be distinguished by a dark line, where little light is reflected, next to a light line, where a lot of light is reflected. I counted the combination of a dark line and a white line as one scratch.

I repeated this process a number of times. Usually I counted slightly different numbers of scratches, but the deviations from the average were not very large.

Because this is such an error-prone and subjective process, this post contains all of the photographs I used, both the original photographs of the edge made by Clay and the 0.01 inch wide portion of the edge blown up 5 or 6 times. I created the latter images by making a screenshot of the Photoshop photograph at 500% or 600% and saving it as a JPEG file, which introduced some artifacts.

The results

Below is the number of scratches I counted for each paste. I calculated the scratch width by dividing the width of the portion of the edge (25.4 micron) by the number of scratches.

Paste Number of scratches Scratch width (micron)
3.5 micron 18 1.41
5 micron 18 1.41
10 micron 14 1.81
14 micron 17 1.49

Based on these results, I think the scratches made by the Wicked Edge diamond pastes have a width in the order of magnitude of 1 to 2 micron.

If that is true, it would not only make them ideal stropping pastes for after the 1600 grit stones on the basis of their burnishing qualities. It would also make them ideal stropping pastes for after the 1600 grit stones on the basis of their abrasive qualities.

The pictures

Below are the pictures I used. Please try to count the scratches for yourself (or conclude that it is not possible and that the entire enterprise is silly). If you send me an email, I can provide you with the Photoshop files that have a higher resolution than the pictures in this blog and have no artifacts.

Edge after stropping with 3.5 micron diamond paste - by Clay Allison.

0.01" portion of the edge after stropping with 3.5 micron diamond paste, blown up several times. I counted 18 scratches.

Edge after stropping with 5 micron diamond paste - by Clay Allison.

0.01" portion of the edge after stropping with 5 micron diamond paste, blown up several times. I counted 18 scratches.

Edge after stropping with 10 micron diamond paste - by Clay Allison.

0.01" portion of the edge after stropping with 10 micron diamond paste, blown up several times. I counted 14 scratches.

Edge after stropping with 14 micron diamond paste - by Clay Allison.

0.01" portion of the edge after stropping with 10 micron diamond paste, blown up several times. I counted 17 scratches.

Is this completely silly?

When I was doing the exercise I describe here, I often wondered whether it was not completely silly what I was doing and whether the results bore any relationship to reality. I needed a reality check.

I therefore decided to also do the exercise with a Wicked Edge 1000 grit diamond stone and a Chosera 10K stone.

I used a picture of an edge I had sharpened myself with the 1000 grit diamond stone.

Edge after 1000 grit stones.

I rotated the picture so the scratches were vertical and cut out a 0.2 mm (200 micron) wide area of the edge.

0.2 mm portion of the edge after the 1000 grit stones, blown up several times. I counted 20 scratches.

I counted 20 scratches. On an area 200 micron wide, that gave a scratch width of 10 micron. That is more than the 7 micron the 1000 grit stones are listed for, but it is of the same order of magnitude.

Then some really fine scratches made by a Chosera 10K stone. I picked a photograph by Clay from the earlier mentioned thread on the Wicked Edge forum.

Edge after the Chosera 10K stones - by Clay Allison.

I again rotated the picture and cut out a 0.01 inch (25.4 micron) wide area of the edge.

0.01" portion of the edge after the Chosera 10K stones, blown up several times. I counted 32 scratches.

I counted 32 scratches, amounting to a scratch width of 0.79 micron. That could well have been caused by the 1.74 micron particles the Chosera 10K stones are listed for in the grit comparison chart. At least they are of the same order of magnitude.

3 thoughts on “Counting scratches: abrasion by the Wicked Edge pastes

  1. Mark,
    This is fascinating and really well done. I think the next step is to re-image the scratches, this time starting with a completely blank slate, as clean an edge as possible, before creating the scratches with the media in question. I’ll get to work on this next week. I think with this method and the new microscope, I should be able to provide you with some even better quality images for your study.
    -Clay

  2. Pingback: Wicked Edge Micro Fine ceramic stones: first impressions | Molecule Polishing

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