Those are interesting questions, Nick.
It is indeed possible that the spine wears at the same rate as the edge bevel, which would not alter the bevel angle. But, being in the habit of measuring blade and spine width to calculate the bevel angle on every wedge I've honed in the last 2 years, I can tell you that this is never the case when one turns up with uneven hone wear like that. Actually, when you look closely at that razor you can see how the spine is worn significantly wider than the bevel. Enough to indicate an altered bevel angle.
Shall we approach this more theoretically?
Let's consider a razor. Lay it flat on a hone. Due to the shape of any razor, the weight is not evenly distributed over both points (spine wear and edge bevel) that make contact with the hone. A mathematician can calculate it in detail, but I think that we can agree that more than 3/4 of the entire weight, even of a beefy wedge, rests on the spine. If would be honing with just the weight of the blade, that would certainly correlate to the spine wearing faster than the edge. But we're applying some pressure of our own, right? But that doesn't necessarily even things out: many hold the razor only at the tang while sharpening. Since the tang is directly connected with the spine and not with the edge, the exerted pressure will favor the spine over the edge. One could apply some serious torque to counteract, but it's not something I often read about... So far, all valuable reasons why the spine is expected to wear faster than the edge bevel. We can put a finger on the blade, to distribute pressure more evenly balanced (that is what I do while performing halfstrokes). But my measurements still show that most wedges with widened bevels near tip and shoulder have significantly reduced spines.
There's also the argument of blade curvature. I think we all agree that those old Sheffields were manufactured with a smile. So the blade was already smiling when new, when there was
no widened bevel and spine wear at the tip. This we know, because there are so many other Wade and Butchers of the same model without the widened bevels that we see on the discussed razor.
I think we can agree that someone honed it that way at some point (probably due to a - in my opinion - wrong habit that he persisted over many sharpening sessions). If it was the kind of equally balanced wear that you would expect, the smile would be even more outspoken than it is right now. Let's look at a drawing to illustrate this claim:
Equal spine and bevel reduction results in a reduction of the blade width as well. Emphasis on spine reduction results on less reduction of blade width. I think we see the latter in this case. But even if I'm wrong, there never is any reason to put more wear on the tip of a razor than on the rest of the blade. What we see is, in any case, a very clear example of such unnecessary wear.
Now, about the consequences.
Let's talk about bevel width first, because, whether I'm wrong or right with my statement about that razor having a reduced bevel angle near the tip, a locally widened bevel IS what we can see here, without any further discussion.
There are two distinctions between wide and thin bevels. The first is the speed at which they can be abraded. A thinner bevel will hit its peak way faster than a wide one. This has, once again, everything to do with the distribution of applied honing pressure. On a wide bevel the pressure is spread out over a wider surface. The effect is dual: the hone works at a slower rate and on top of that it must remove a larger total amount of steel, to accomplish the same "refinement". This leads to an exponential rate of edge development slowing down, when bevel width increases.
Nonetheless, you might think, let's just do more laps then. But how are you going to do that without also abrading the already keen middle part of the razor any further? Luckily a Coticule doesn't overhone, so it's a possibility. But it'll remain a frustration to wait on the wide part to follow, preventing to loose the smile in the process.
Loose the smile in the process??!?
Indeed. While you are working to make the wide bevel sides at the tip to join and gain keenness, you're reducing the width of the already keen middle part of the razor. Your only solution is to apply more pressure to the tip, which achieves your goal, at the expense of the condition worsening even further. That is how I think the razor arrived at this point in the first place. And with art, that has not much in common.
The second, worse, distinction is that wide bevels, from a certain point onwards, do not take the same high keenness than bevels that are within reasonable limits. When sharpening, there are two things happening (that's the third time we have 2 principles in one process, but I can't help that either
). The edge is pushed over the hone's surface: for the microscopically fine bevel tip, this is not an easy ride. The keener the edge, the finer the bevel tip and the more it becomes affected by collisions with swarf, stray honing particles and microscopic protrusions at the surface (exactly the same protrusions that do the actual abrasion). This is a
deteriorating force. At the same time, steel is removed from the bevel faces. Obviously this is the
"keenifying" force. And now comes the catch: on a wider bevel, the keenifying force slows down, while the deteriorating force remains constant. As the edge becomes increasingly finer, it becomes more affected by the deteriorating force, and at a certain point the keenifying force can no longer make up for what the edge looses. The hone has reached its limit, the edge is maxed out. A few final laps with light pressure or performed in stropping direction, may push the limit a little bit further, but not much. On a wider bevel, the limit will be reached sooner,
at a lower level of keenness, because there simply is less "making up" for equal amounts of tip deterioration. The limit that can be reached is always a function of hone, steel properties and bevel width. By the way: this is the big reason why Unicot remains easier. It always works on a very narrow bevel. Most wedges are honed with tape nowadays, to assure good keenness. And even then they are often seriously hit with pasted strops, which have their own strategies to work around this issue.
So far for the troubles with a (partially) widened bevel, regardless of bevel angle. But I still believe the discussed razor has a lowered bevel angle as well.
After 3 ages of straight razor production, we see that all manufacturers have arrived at a bevel angle that centers around 17 degrees (I am referring the enclosed angle between both bevel faces, and not to the angle between the axis of the blade and the surface of the hone, as often used in knife an tool sharpening). The bevel angle doesn't need to be much lower for the edge to become weak and brittle. Microscopic chipping, both on the hone and during the first shave, is to be expected. Even if you manage to get get such a lean bevel sharpened without crumbling, edge longevity will be extremely poor, because the edge simply lacks the support of enough steel to cope with the occurring stresses during a shave.
And for these reasons, I say it is nonsense to call the discussed razor skillfully honed. I do not claim that it can't be turned into a good shaver. Any piece of good steel with the correct hardness and temper can be turned into a good shaver. There's the use of tape and also pasted strops have their own artifices to deal with the aforementioned issues. But it wasn't exactly requisite to put that heavy spine and bevel wear on the tip of that razor. In my opinion it's a butchered razor.
Kind regards,
Bart.
