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Effect of oxidation on sharpness
It's a commonplace that edge sharpness worsens from the moment we've deburred it and measured, through the first day, even if the knife doesn't cut anything.

BESS sharpness score of a freshly sharpened edge is always better than that 1-2 hours later, and the worst is in 12-17 hours after sharpening.

It is practically important to know what drop in sharpness comes from oxidation (i.e. increase in BESS reading).
Knowing that, a BESS score worse than what we could explain by oxidation will indicate either presence of a microscopic wire/foil burr that folds to one side of the edge with time, or the edge apex overheating & softening that leads to the apex bending to one side, or both.

I've done a series of tests on stainless steel to quantify this change in sharpness, and found that a completely deburred edge scores by 5 BESS more in 1-2 hours, and by 10 BESS more in 10 hours.

Recently I came across a Japanese study Analysis of oxide layers on stainless steel that has data on chrome-oxide layer/film thickness. This film thickness is temperature-dependent, and also acidity-dependent. I double-checked the common buffing compounds data sheets, their pH is neutral; next week am getting litmus paper to check actual pH of the mix of the honing compound and swarf on my paper wheels.

Initially the chrome-oxide film thickness is 3-5 nm, but if mechanically polished and heated to 400 C degrees, the film thickness reaches 20 nm - isn't that exactly what is happening to the very edge when we deburr it on a felt or paper wheel at high RPM?
This is in line with the BESS score worsening by 5-10 BESS that I observed - BESS edge sharpness testers show edge apex radius in nm, and that extra 5-10 BESS is the 5-10 nm thick chrome-oxide film added to the radius.

Based on my tests, and understanding of the data in that study, I concluded to myself that any worsening of the BESS score up to 20 BESS can be attributed to oxidation; but worse than that  shall be attributed to the wire burr or edge apex folding.

I've re-read what Mike writes about the wire burr in the KN100 Operating Manual, pages 39-42 at

First, Mike noted that it takes 6-8 hours for a straightened wire burr to regain its folded position due to metal memory;
Second, complete removal of a wire burr improves BESS reading by 50-60 BESS; and
Third, a stropped edge left for a couple of hours will score 10-15 more - I now attribute this to oxidation chiefly.

To better understand what I've read, I did another series of tests on an edge that had a near continuous wire burr seen under a microscope - if you strain your eyes really hard, you can see that tiny burr along the edge apex on the photo below.

In 1-2 hours the BESS score worsens by 5-30;
In 10-12 hours by 45-50 BESS.

[Image: wire_burr_.jpg]

Practical use of those findings is in detecting a microscopic burr by simply letting a sharpened blade lie idle for 10 hours, and then taking a repeated BESS reading - a score increase by more than 20 BESS is indicative of the burr.
If such a knife is put to use, its cutting performance will quickly drop due to the burr and apex rolling.
To fix this, I take the blade to a paper wheel with a 0.5 micron abrasive and do just one light and quick pass each side at a higher angle (e.g. an edge of 15 dps I hone at 15.4 degrees). After that, the BESS score immediately improves by at least 30-40 BESS, then in 10 hours worsens by 10-15 BESS (oxidation), but then stays unchanged even when checked days later.
Very well thought out and presented KG and thank you for publishing the results of your experiments. Our BESS Partners will find this particularly interesting we think. For those of you who may not be familiar, BESS Partners are those companies, usually industrial, that include the BESS logo on their packaging and provide certified BESS numbers on or with their finished edges. BESS numbers are often specified by the end user of the product. Oxidation and metal memory are factors that must be considered by both BESS Partners and their customers in that  edge sharpness may degrade even in just the time consumed by the shipping process. It is a very common circumstance where both supplier and end user own and use edge test instrumentation. This work will help put both on the same page so, once again, thank you KG for your contribution! We're going to ask that Admin put this up as a sticky.
(By the way, the Knife Grinders company is a BESS Partner as well)
Thank you, Mike.
I believe Machine Knives Australia is a good candidate to become the 2nd BESS Partner in Australia, give them time to appreciate your testers potential.

The terms "wire burr" and "foil burr" are generally used as interchangeable synonyms.
But we can discriminate them by microscope, and label "wire burr" the first image of the two below, and "foil burr" the second.

[Image: wire_burr_.jpg]

[Image: wire_burr.jpg]

[Image: wire_deburred.jpg]
KG, thanks for your very interesting post.

Let me apply model BESS measurements, roughly based on Mike’s data, on the estimation of edge apex width.

Assume a stropped blade with 250 gf score. Repeated testing after 2 hours shows 260 gf.
What we can say about apex width?
If 250 gf corresponds to 500 nanometers of apex width,
than 260 gf corresponds to 520 nanometers of apex width.

If we attribute the small sharpness drop to oxidation processes at the edge, than we can say that on each side of the edge a 10 namometers thick layer of oxides has grown.

But be careful. When another retesting after 8 hours shows again 260 gf score, we would have to conclude that the oxidation rate dropped dramatically or look for another explanation.


If I correctly read the studies on the stainless steel oxidation available online, a complex chrome-oxide film forms within first hours, and prevents further oxidation and rust; its thickness stays the same after that.

What you say about the oxidation rate may have place in rusting carbon steels - especially the red rust Fe2O3.

My estimates and concern are about the stainless steel with at least 13% Chromium content, as this is what the majority of my customers have their blades of.
I set oxidation-related drop in sharpness to 20 BESS, given the 5 units resolution of the PT50B used at my workshop.
Yes, KG, you are correct. When the scale is formed, it slows down further oxidation. The oxidation of stainless steel is more complicated than of carbon steels because in addition to iron oxides hematite and magnetite also chromium rich oxide is formed.

I would be interested to read more about initial stages of steel oxidation at room temperature. Most papers I have seen were describing the situation at higher and high temperatures.

Just out of curiosity. Two decades ago US Nuclear Regulatory Commission reviewed low temperature oxidation of carbon steels intended as package materials for radioactive waste repository at Yucca Mountain, Nevada. In this compilation the oxidation kinetics was extrapolated to 1000 years at 250°C (480°F). For a low carbon steel with fine pearlite microstructure they calculated only 4 microns of oxides.


You got our attention Jan with your mention of Yucca Mountain. Two of us here at EOU worked with Lawrence Livermore on that project some years ago. Our Job? To measure how much the rock at the mountain, under extreme heat/pressure, could expand before it cracked. We built the instrumentation and tested it at the site but the Livermore boys set it up so I never did actually go inside the repository. I know that the site was selected, in part, due to the scarcity of both surface and groundwater in the area. This is all likely neither here nor there because the NRC study probably wasn't actually carried out inside the mountain but rather, duplicated the conditions inside the mountain. In any case, don't you think that at 250C  it would be a pretty dry atmospheric environment and hence, not conducive to the formation of rust/oxidation? As you may know Jan, like Arizona, decaying radioactive material is a dry heat.

I do know, however, that the contingency plan for an overheated storage compartment was to flood the compartment with water so perhaps the NRC study contemplated this possibility.
Mike, what a strange coincidence! I agree with you what concerns the "pretty dry environment". Also the temperature 250°C probably includes large margin. In this country we model the repository processes for much smaller initial temperatures.

The review of carbon steel oxidation I have mentioned was prepared by prof. Robert Rapp from Ohio State University.

The NTS is for me a place with a troubled past, contaminated with long living isotopes for tens of thousands of years.
In my thinking, the high level waste repository would be a suitable usage of this  area.



Mr. KG,

Nice microscopy!  What scope are you using?
These images were taken with an Adonstar USB microscope

As you noted elsewhere, so hard to cast light at the right angle for a good image.
But I wouldn't recommend the Adonstar, I struggle with it, the stand is wobbly.

Because of that I bought another one, twice more expensive, still not happy with the resolution

Yet have to find a satisfactory one without getting broke. I remember liking Jan's BRESSER microscope that he got as a present from his children I believe.
Jan, are you happy with yours?

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