That mirror surface

[paulsen]

My first two successful sharpenings with a Coti went reasonably well. I ended up with two razors that shave just fine.

But this is not a 100% success story.

Looking at the bevel under a 10x loupe I did not see a nice mirror-like surface that I see on razors I have had professionally honed so I finished up with a 12K Naniwa and did get a nice surface from that.

The only sharpness test I used (other than getting a good shave) was shaving arm hairs, which worked well.

So, what is my problem?

• 
  [li]Is my technique (or patience) just not up to it yet?[/li]
  [li]Am I expecting something that just isn't going to happen?[/li]

Don't get me wrong. I am actually quite surprised and happy with the results I got and now have a very satisfying feeling that I can "take care of myself" as far as straight razor honing is concerned.

 

[Bart]

Coticules don't create a mirror polish. That's nothing to worry about. A shiny surface is just a shiny surface. It doesn't tell anything about the keenness of an edge or how smooth it shaves. Allegedly, in the Japanese sharpening tradition a hazy finish is often preferred over a mirror-like one. I'm not that well informed about it, so let's leave it at that.

The Typical surface finish left by a Coticule is dual: Use of slurry leaves a pretty blurred satin finish, while use of only water on top of the hone creates the shine of a mildly fogged mirror.
A picture at 40X optical magnification helps to understand the difference:

The "slurrified" surface looks almost as if it was micro-sandblasted. The "watered" surface caries an extremely shallow scratch pattern (which explains why a Coticule on water is so slow), that looks wavy, with an absence of sharp transitions. Because of the waviness, the light is not reflected in one direction, hence it leaves no clear focused mirror like finish.
The long stray scratches running through both the primary and the secondary bevel are caused by the strop. Probably by small fragments of steel embedded into the surface of the leather. One of the reasons to use a linen strop before the leather. The linen embeds such small fragments, that occasionally get knocked off a razor's edge, better into the "depths" of the fabric. This leaves the leather strop cleaner.

For comparison, let 's also look at a Naniwa Chosera 10K edge. This one carries a double bevel as well, both parts polished on the Chosera:

Notice how the surface is much more mirror-like? Yet at the same time the pattern has more sharply defined valleys that that left by a Coticule. If you look well, you'll see how the edge has a bit of sawtooth pattern. The Chosera edge cuts more aggressively than the Coticule's. It can be perceived as sharper, but also as harsher. I believe that's strictly due to the teeth.

Best regards,
Bart.

 

[paulsen]

Bart,

Thanks! Great pictures and explanation. Looks like I did even better than I thought.

Next time I'll try using just the Coti and skip the 12K.

Bob

 

[Bart]

Bart,

Thanks! Great pictures and explanation. Looks like I did even better than I thought.

Next time I'll try using just the Coti and skip the 12K.

Bob

I bet that Naniwa Superstone 12K is very much like a Naniwa Chosera 10K, when it comes to finishing results.

It's certainly worth to compare the finish of your Coticule to that of the 12K. To do that, just refinish your razor on with 50 laps or so on a Coticule with just water. There a good chance you'll find that edge a bit gentler on the skin.
You can bounce back an forth between the 12K and the Coticule finish during a number of shaves, till you made up your mind what you like best. That's certainly a fun personal experiment.

I find a Coticule hard to beat for edge finishing, but reaching the required keenness can be a challenge. A 12K is certainly useful to have a bit easier access to that kind of keenness. It does remain a problem for many inexperienced Coticule users to bridge the gap between slurry-limits and what's required to finish on water. A high grit synthetic is certainly an efficient option to fill the gap.
Translated into a progression, it looks like this:
1. Coticule with slurry till the bevel is perfected.
3. 50 -100 laps on the Naniwa 12K till the edge pops hanging hairs. (it seems like a lot, but you need to realize we're not just polishing, but actually remove steel for a keener edge)
3. Finish with 30-60 laps on Coticule with water.

If you try to use the Dulicot method to make the razor as keen as you can manage, you'll need less steps on the Naniwa. In time, one can learn to get there without the Naniwa 12K, but that does demand for perseverance and experience.

Kind regards,
Bart.