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A theoretical discussion about honing particles
"Honing a razor is often said to be no rocket science." A much quoted statement on Basic Honing Topics section of SRP. It's as true as false, I guess.
Grab a Norton, read the recipe, practice a little and a shaveready razor dawns at the horizon.
But beware, because the lure of ever increasing sharpness lies literally "just around the corner" and soon the aspiring honing finds himself on a quest for more than shavereadiness. In this new realm, whiskers should be swept off the face, leaving the skin as smooth as that of a newborn baby. At this point, many questions arise. Does the grain of the steel matter? Which forces are at work during the sculpting of the cutting bevel? How do they relate to the hardness of the steel? How to they relate to the plasticity of the steel? etc, etc... This has been the subject of serious scientific study. The work of professor Verhoeven at the Iowa State University is often cited in that regard.
Verhoeven reports that edges are not only formed by abrasive action, as we run a razor over the hones' surface, but also undergo plastical deformation. This principle makes it nearly impossible to fully understand how a particular hone will affect an edge. But since most of the action seems to come from abrassion, and it is the easiest to figure out, I'd like to elaborate on that a bit, just for the sake of having an informative discussion.
About particle size and grit counts.
I'm no big fan of grit counts. They raise confusion. For starters, few realize that doubling the grit count doensn't half size of the scratch marks. Let's supose a grit count of 4000. That's 4000 particles per square inch. If the particles were touching eachother, we can easily calculate their size. The square root of 4000 is approximately 63. This means one inch contains 63 X 63 particles. One inch is 25400 micron. 25400 divided by 63 is 403 micron. It is clear that most 4000 grit hones have particles much smaller than 400 micron. That's because they are surrounded by the substance that binds them together. A 4000 grit hone could contain particles of any size from 0.5 to 400 micron. (I hope someone reviews my math)
Now, let's suppose that a manufacturer has the decency to keep his hones' particle sizes relative to his grit counts. Would this mean the particle size halves everytime the grit count doubles? Not necessarily. The square root of 8000 is approximately 89, leaving us with a mesh of 25400 divided by 89 equals 285. Hence, when the grit count doubles, the particle size decreases with a factor 1.4. Otherwise put, when the particle size halves, the grit count quadruples.
Unless, they're all just doing whatever they think is the best for marketing their hones.
Which is more likely than my math excercise...
Between different brands, I wouldn't bet my money that 6000 is finer than 4000.
Even so, there's more to define the properties of a hone than its grit count. Particle shape and aggressiveness are not to be underestimated. I'd like to illustrate this with a drawing that compares small, but deep scratches of a fast hone with a wider but more shallow and rounded scratch pattern. I was after a better understanding why Coticules create such fine edges with relatively big particles when I started making this drawing.
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Folks, there's no need to work so hard!
There are standard ways to relate Grit, Mesh and Particle Size. Please see the table below, it's just that simple. Bart, please don't burn up your slide rule on this one, it has all been worked out! Enjoy gents. :w
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Grit, Mesh and Particle size
Grit is a measure of the particles that go through a certain size mesh and as such can be related to a particle size. The relationship can be derived from the chart I published in my first post to this thread above. It is a logarithmic power law equation and when expressed as such it has a better than 99% fit. It isn't simple but it can be understood. As you can see, though many have asserted that a Belgian Blue has a 4000 grit and a Coticule an 8000 grit, the actual grit that relates to these stones is more like 1200 to 1800.
