I defended his approach in the first video, but if that second video shows something, it's that Mr. Carter only has a limited understanding of sharpening. Considering that he's a bit too obviously seeking self-promotion (the opening sequence of the video is so undeniably preconcstructed that it becomes pathetic), I 'm really not sure that he deserves the attention he had on at least four different shaving forums.
Hence I'm not going to spend too much attention on Carter, but will address some "facts".
1. edge leading vs edge trailing sharpening.
It is an erroneous oversimplification to think about sharpening as merely the result of abrasion. Abrasion can be defined as materlal removal, in our case caused by a scraping action of sharpening stone particles that are harder than steel. This scraping causes grooves. The removed material ends up as debris on top of the hone. Usually it goes in suspension in the water (or whatever fluid) we use.
If sharpening was just that, it would be easy to understand. When two corrugated surfaces meet, their edge is a sawtooth line formed by both superimposed groove patterns. Make the grooves shallower and you'll get a cleaner edge line, Make the grooves less wide, and you'll get finer teeth. It would not matter if both bevel surfaces were created in edge leading of edge trailing direction, because contrary to what Carter states in his video, the particles of the hone do not protrude beyond the depth of the grooves. If the particles were higher, the grooves would simply be deeper. It is the reason why sharpening usually works with different grits. Deeper grooves mean: more steel removal.
But there is more going on than merely abrasion. Not all the scraped steel loosens and ends up in the puddle of fluid on top of the hone. Especially, but not exclusively, near the end of each groove, part of the scraped steel "shavings" remain attached to the steel body we're sharpening. This process is called: burr formation. Knife sharpeners typically use their fingers to feel for the presence of burs at the tip of the bevel. They read it as proof that both bevel planes are actually meeting up with each other. And they usually try to knock off these burs by dragging the edge through a piece of wood, or by reducing them on a bench strop loaded with a very fine sharpening paste. It is also the reason why sharpening is considered to be better done in edge leading direction. Professor Verhoeven of the Iowa State University compared bur formation near the bevel tip in both edge leading and edge trailing directions, and he could confirm what most sharpeners already observed. Bur formaton is more apparent in the edge trailing direction. It is by many (including myself) believed, that edges that are made from primarily bur-like material, are more prone to chip during use and tend to dull prematurely.
Another factor in sharpening is called "plastic flow". This is somewhat related to burr formation, and more closely related to
burnishing (
read about plastic deformation and burnishing)
At the sub micron level (a shaving edge has a tip radius of 0.5 micron and less), plastic flow become increasingly more important in the shaping of the edge. It is also the most probable cause for Verhoeven's observation that inspite of abraded grooves, the edges he photographed with scanning electron microscopy were not as toothed as the principles of abrasion would dictate.
Which brings us at paragraph 2.
2. Do not rely on macroscopic emulation to understand the micro-physics of sharpening.
While it can be fun to grate cheese in a bevel shape and rub candles over a leather belt, it is very unlikely that such actions will predict anything about sharpening hardened steel. Not only because different materials behave differently, but because even the same material will behave differently at atomary level than at larger scale simulations. Even if we could build a razor on a 100X larger scale, stropping that razor on a 100X larger strop would not mean that we would get a 100X better view on what's actually going on during stropping.
Which brings us at 3.
3. Stropping on leather = not stropping on pasted leather.
Stropping on leather probably relies on 100% burnishing. Verhoeven found no evidence of significant abrasion in clean leather, while he observed ample abrasion when the strop was pasted with Chromium Oxide. Someone once argumented that one can remove burs with a leather belt, but grabbing a bur and breaking it off is not the same as
abrading a bur.
It also struck me how Carter did not strop the candle at all. He actually rolled it over the edge. It's easy to disproof the usefulness of a hanging strop by using it in a way it should't be used at all.
4. Tape is not traditional.
It really is not. But something not being traditional is only a valid argument for those who want to stick close to tradition. There was a time when full-hollow grinding of razors was "not traditional". I am glad someone decided the fuck with tradition.
5. Razors wear uneven when sharpened with or without tape.
Carter forgat to mention that tape can be used to create a secondary bevel late in the sharpening process. As such it won't have much influence on preventing the spine to wear "as it should".
But even then, or when no tape is ever used, it is far too easy to assume that both the spine and the blad are going to wear at a rate that keeps the bevel angle constant. Let's consider some facts: A. the spine is heavier than the edge. B. the hand applies pressure at the tang, which is directly connected with the spine and only indirectly to tthe edge. C. Rockwell testing of a small collection of straight razors
revealed that several of them were softer at the spine. (It has been specualted that during the quenching, the spine with its greater mass cools more slowly than the thin blade)
Those three facts all indicate that the spine may very well wear faster than the edge bevel. But even if the sharpener tries to counteract by applying torque while honing, who dares to say that he can balance the applied pressure with such great precision, and can do that for each razor's individual needs?
Furthermore, should the spine be proven too thick at some point in the lifespan of the razor, it is easy to tape the
edge, and grind the spine a bit thinner on a coarser hone. The opposite however, is not so easy to remedify. Not that I wish to advocate the use of tape for all honing. But to criticize tape with the arguments Carter used, is no display of 3000$ worth of knowledge.
6. Flat bevel vs convex bevel.
As already mentioned a cutting edge can be described as the line where 2 surfaces meet. We call that geometric shape "the bevel". Whether the surfaces are flat, convex or even concave, is of no real consequence. It only results in a different angle at which both surfaces meet each other. We could theoretically sharpen a razor on a hone with a hollow radius. The resulting bevel would be arc-shaped (convex), but it can be just as keen as a flat bevel created on a flat hone. Honing with pasted strops actually achieve just that, and the loom strop is created as a sharpening tools that allows good control over the tension, hence over the curve of the strop.
The more or less official sharpening methods of Dovo (Germany) and Thiers Issard (France), rely on the use of pasted strops, and also Maestro Livi (Italy) uses and sells his own make of loom strop for that purpose. If these manufacturers have designed their blades with such great care as Carter assumes, it is only fair to assume that they've established their ideal angles with their particular methods of sharpening. Convex bevels having a bit wider angle than flat bevels, a layer of tape add to the spine may be closer to the intended angle for honing on flat stones. Not that I think it matters, because nothing indicates that these manufacturers are so strict about the design of their razors. Something that centers around 17 degrees plus or minus 3 degrees, is what we found a few years ago during a survey of measuring bevel angles on a wide variety of razors.
In conclusion, I personally don't care for Mr. Carter's sharpening methods. I have no doubt that they work for his intended purposes. It is great that he shares and documents his procedures, so that those interested can try to reproduce his results.
But once something is shared publicly, one must also accept that it may be criticized publicly. As long as the discussion is conducted with honest arguments, it can only serve the greater good.
Bart.
: In fact with your permission Emmanuel I may steal it and use it as a signature.
