it's been a while but finally I can present some results with the slurry stones that Bart sent me.
I have to say that I struggled quite a bit. After playing around for a while I noticed that the differences made by the various slurry stones are not huge. An observation that was confirmed in my first "experiments". This initial observation gave me a hard time in crating experimental setups that would yield meaningful, reproducible, and significant results. However, after Bart gave me a little kick in the butt (thanks Bart) I finally managed to get myself going.
When I thought about how and what to test I asked myself which properties are of interest to me with respect to honing and shaving quality. I concluded that the following set would be a good and representative choice, not the least in dependence with Bart's rating scheme:
- Abrasion capability (speed)
- Finishing properties
- Surface appearance / scratch pattern (ok, that's more the techie approach …)
Generally, I would expect to see the biggest influence of the slurry stone when most of it is present while honing. This is the case at the very beginning when the slurry on the hone is thickest. Hence, I would conclude the differences with respect to abrasion are the most dominant and the easiest to reveal. Sharpness already starts to rely more on the properties of the hone. Maybe less in the early stages when there is still thick slurry present but certainly later in the honing process when the slurry is diluted or washed away. I expect the least significance of the slurry stone when it comes to finishing. By definition this is done without slurry and therefore there cannot be any direct influence of the slurry stone. It is however conceivable that the preliminary work of bevel setting and refinement does show indirectly in the final edge.
The surface appearance might be an interesting thing to have a closer look at. If I get my hands on one of those mini-microscope I might give it a try …
So I started yesterday with some honing to test for abrasion. On one hand because I expected the most significant results but on the other hand because it probably requires the least honing skills. Human factors are not for nothing the largest source of bias/errors in any experiment.
After I posted I noticed that I confused x-strokes and half x-strokes.
So, whenever you read "x-stroke" in the post or in the picture database just replace by "half x-stroke"
When sharpening on slurry we expect the slurry to have a significant influence on the abrasion speed. The composition of the slurry should therefore be a relevant factor on this abrasion speed. Depending on the hardness of the slurry stone and the actual hone there will be different shares of both present in the slurry. If the slurry stone does make a difference then we would expect it to be the more significant the more the slurry consists of slurry stone (awkward formulation, isn't it?)
- Create thick slurry as required for first stage of unicot/dilucot
- Do a defined number of x-strokes
- Repeat with different slurry stones
- Repeat with different hones
- Criteria: Discoloration of slurry, Honing "feel"
Slurry stones: La Veinette, la Petite Blanche, la Dressante, sandpaper (or dmt)
Hones: My own la Grise, and from Bart la Verte and one unknown vintage coti.
Razor: An eskilstuna 4/8 from ebay
Annotations to the pictures and the photo album:
The pictures are organized in three folders. Each folder contains the result for one hone and is named accordingly. Naming convention for the pictures is "Name of hone _ name of slurry stone _ number of strokes". If you click the previews you get a larger picture with text up left.
With an eye on comparability the white point for every picture was set at a fixed value of 6000.
Results for la Grise:
I used this coti because it is by far the slowest of the four I have with me right now. Bevel setting on this piece is next to impossible unless you take an extra vacation for honing. It is also quite hard and yet it has a somewhat "bumpy" feeling when honing (notice: send coti to Bart and see if he can reveal the magic).
As you can see, after 2x20 x-strokes there is virtually no discoloration in the slurry. It does not matter what is used to create the slurry. They all look pretty much the same and that goes even for the one where the slurry was created with sandpaper (kinda auto-slurry).
Even after 2x40 x-strokes the discoloration is very vague. See why I said that rock is REALLY slow! There are some very slight shades of difference in the pictures but I would attribute them more to exogenic errors (slurry amount, camera position, honing mechanics).
So if the expectation was that a fast slurry stone would speed up a slow coticule SIGNIFICANTLY this expectation can in this case be denied. There was however a slight difference in the honing feel which I will come back to in the la Verte section.
Results for la Verte.
This is a very peculiar piece of coti. Apparently Bart has litteraly picked it up somewhere along the way, strolling around in the Ardennes (jealous anyone? Imagine beefing up your budget by simply stepping out in your backyard and picking up some Eschers to sell them on ebay …:w00t: )
The coti is EXTREMELY hard. Almost like glass and with very minimal feedback when honing. It is so hard that it would not raise decent slurry with sandpaper so I had to use my DMT instead. Yet, it is not slow. Among my cotis I would surely rate it moderate. Even with plain water I can clearly see metal debris coming off the blade after 20 strokes. Being so hard the Verte would make a good test specimen because the slurry would consist to a major part of the slurry stone.
I also did a set of 2x20 and 2x40 x-strokes each. Again, with 2x20 x-strokes I would not dare to state a difference in the slurry color. In the 2x40 set I would give the three trials with slurry stones a slight advantage over the one with DMT - but really very slight!
Interesting was an observation I already made with la Grise. DMT, la Veinette, and la Petite Blanche pretty much gave the same feedback while honing. Very little that is. Not so la Dressante. This piece was able to change the feedback. Instead of glass-like it gave the clear sensation of abrasion, almost like on a very fine sandpaper. While this apparently did not influence the abrasion speed by much I still felt that this can be very helpful. Especial for novice honers it is not always easy to guide the blade properly. But this somewhat more intense feedback may give you a better control, because variations in blade position and pressure can be felt much better.
Results for the unknown vintage coti.
This coti was rated fast by Bart. A rating that I would surely confirm. It also seems quite a bit softer than the other two but it is still not an auto-slurry coticule. Based on previous experience I juped the set with 2x20 strokes and only did 2x40.
In these pictures I would rate the difference between slurry stones and sandpaper a bit more pronounced tha in the previous set. The one with la Dressante seemed to stick out a little more. this may not come out well enough in the picture but during honing it did look like that the individual strokes did produce more metal shaves per stroke. Yet again, the differences are not huge and having a fast coti anyway the bevel setting process will most likely not need a much different approach.
I have to say that I am a little puzzled by the results but they do confirm my initial impression as stated at the beginning of this post. It is a proven fact that a coti used with slurry is considerably faster that when used without slurry. So the slurry does have a big influence. But all in all the influence of different slurry stones on abrasion speed seems to be minor if existent at all. Even more confusing is my observation that the difference is the more significant the faster the coticule itself is. I would have expected the exact opposite.
One possible explanation for this fact might be that the abrasion speed is not determined by the composition of the slurry per se. Much more it seems that the metal removal is still done mainly by the coticule. More than doing the abrasion itself the slurry only seems to serve as a measure to enhance the coticules own capability to remove metal. Or in other words: Not the slurry seems to do the work. No matter what the slurry is made of it is still the coti that does the work. The slurry only seems to help make it do its work faster than without slurry.But how?
Yes, when honing on a slurry there will be more garnets per area present that remove metal. The underlying coticule has garnets embedded that stick out the matrix. The slurry may then fill the voids between the embedded garnets and therefore increase the number of garnets per area. This backs up the fact that a coticule with slurry is faster that without. On the other hand this would also suggest that the abrasion speed would increase significantly on a slow coti! Hmm, wrong theory it seems …
I've been thinking for a while now and hypothesizing on different theories but I just can't figure out a mechanism that fits my observation. So here you are gentlemen, maybe one of you can find the trace.
If I was to summarize in a nutshell if different slurry stones do make a difference:
Not so much when it comes to abrasion capabilities / speed. Interesting enough, the influence on speed seems to be more dominant on already fast coticules. Yet, I found a quite noticeable difference in alteration of audible and sensible honing feedback - at least for one of the slurry stones and that is la Dressante. And that can be beneficial especially for novice honers because it may help to control the blade better during honing….
What about the next steps. The question about sharpness and finishing remains open at this point. I am not convinced that I am the right man to do these tests. I am still struggling to get a consistently sharp result when using dilucot and even unicot sometimes lets me down if I don't pay close attention. I would however want to try and take microscope pictures of the edge after the above tests and see if the findings can shed some light in the dark.
DISCLAIMER: I consider myself still a quite inexperienced coticule honer. I cannot eliminate the possibility that I completely screwed up :blink: :blink: :blink: and the posted results show nothing but the human factor!
Ok, I'm exaggerating but since the differences seem to be minuscule the human factor must be considered as an important teammate in this game.
And now I gotta run and hone some razors. I recently scored a NOS Escher on a flea market for a "I don't know what this thing is for"-price …. B)