A Coticule is not 8000 grit. That's just - understandable - sales talk, inspired by the grit ranges of popular synthetic hones. Allow me to explain: Coticules typically contain garnets in a 5 to 15 micron range. I think we all agree that the largest particles define the actual "coarseness" of a one. Even a Norton 8K will probably contain particles smaller than 3 micron, which is the upper limit of that hone's partical size. Translated to Coticules, that gives us a grit rating of 1500.
This immediately explains why I keep repeating that grit rating is completely irrelevant when we talk about natural hones, a forteriori Coticules. For it is not the width of the abrasive grooves that determines how well a hone can define an edge, but the depth of those grooves. And even that is only part of the whole picture, as I will explain in the next paragraph. Sure, there is a correlation between width of the paricles and their cutting depth, but different shapes of cutting media can make a *huge* difference. It is possible, perhaps even likely, that larger rhomboid garnets cut shallower than smaller ones, for the one reason that their larger surface area doesn't penetrate the steel so easily. This sheds a new light on why Coticules cut entirely differently than synthetic hones with their acute, yet smaller, abrasive particles. It also explains why Coticules demand a different kind of sharpening pressure than synthetic hones. And it indicates that BBW's with their larger garnets are possibly much finer hones than often intuitively expected.
Another largely ignored factor in the final characteristics of an edge, is the amount of plastic flow, that is inherently different between various hones and pastes. "There he goes again". I can almost hear some of you think that. Nevertheless there is no doubt that plastic flow plays a key role in the submicron world where the tip of a razor's edge resides. If not, every edge would carry a saw tooth pattern, defined by the particle size and shape of the finishing hone or paste. Coticule edges would cary a sort of an S-shaped curve, and synthetic edges fine sawtooth pattern. I once followed that idea, even drew up a 3D representtion of it.
[IMG=600]http://www.coticule.be/tl_files/barts_pics/groove-hypothesis.jpg[/IMG]
While an interesting exercise, the above drawing is pointless, because it completely ignores the effects of plastic flow. As soon as I saw Prof. John D. Verhoeven's SEM-pictures, it became apparent how wrong my drawing was. Verhoeven magnifiied edges up to 3000X with a high resolution scanning electron microscope, and he found no sawtooth pattern, no obvious grooves running all the way up to the very edge, no so-called "striations". What he found was a smooth uninterrupted edge, with a given end-radius, typically arround 0.5 micron for razors. The top of that radius showing a number of elongated burr-like rims. The absence of the expected grooves and teeth can only been explained by plastic flow. As opossed to abrasion, plastic flow does not removes steel, but displaces it, not unlike what we can observe during the cold rolling of steel. It relies on the malleable properties of steel and not on abrassion.
The ratio abrasion/plastic flow is different for each type of working particles. It relies on several factors, interesting enough to treat separately:
1. hardness. Diamond, on one side of the sprectrum, offering a lot of abrasion, and therefor undo's a large part of its plastic action. Chalk, on the other end of the spectrum, being softer than steel, offers minimal abrasion and mostly buffing (read plastic) action. Different hardness is prossibly one of the big factors that makes 0.5 micron diamond paste differ form 0.5 chromium oxide paste.
2. particle shape. Round and smooth shapes being less abrasive and more inclided to roll the steel. This could very well be one of the advantages of Coticule hones.
3. mobility of particles. Particles that are solidly cemented in the surface of a hone, probably offer relatively less plastic action than the more mobile particles on the surface of a pasted strop.
4. applied pressure. More pressure probably favors abrasion. This explains why polishing with buffing wheels, a surface treatment that relies for a significant deal on plastic flow, differentiates between "cutting" (much pressure) and "coloring" less pressure.
I find this all very interesting stuff, but at the same time allow me to be quick to acknowledge, that a well-honed razor, remains a well honed razor, and that I highly doubt any one on these boards can discern between a truly good Cocitule edge and a truly good CrO edge. At least not by one comparative test shave. Perhaps after several shaves, when the difference in longevity between both starts to become apparent. But that has more to do with edge leading (honing) vs edge trailing (stropping) techniques. The difference in feel that is descibed by Stalker in the post above, has more to do with a difference in attained sharpness, than with the actual finishing properties. Attaining keenness is much easier on a CrO strop than on a Coticule. It is one of the reasons why many prefer other sharpening solutions. Sharpening with a Coticules differs so inherently from sharpening on a Synthetic hone or with aid of a pasted strop, that even experience sharpeneers need some time to adapt to Coticule honing.
I would also like to point out that I buy none of the steel/hone paring mythology. The Japanese have also turned tea into a ceremony, that no doubt holds its emotional rewards, but does the end result tastes any different than a non-ceremonially made tea of the same leaves? Even if I am totally wrong with my skepticism, I still don't understand how someone, short of collectioning them, is going to figure out an amount of finishing stones, that takes a Japanese honemaster an entirely lifetime of daily practice to figure out.
Kind regards,
Bart.
I guarantee you that a good Coticule edge will shave any beard without needing any further treatment than stropping it well on linen and leather. If it needs CrO to shave well, then Gary is correct: you've not yet quite squeezed that final bit of keenness out your Coticule, that is so imperative to unleash the true brilliance of these hones.
