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Slurry stone investigations


Well-Known Member

as some of you may remember, I raised some questions on how different slurry stones would influence the sharpening process on the same piece of coticule. As curiosity killed the cat my curiosity actually made me receive a parcel from the honorable SHITCA chairman Sir Bart. It contained two cotis and three slurry stones.
The task will be to answer my above question by doing appropriate tests. I haven't figured out the scientific procedure yet but I guess I'll better get going since the pressure is really on now B)

I do not know much about these rocks and how they are supposed to behave. Bart asked me to post pictures so he can comment on them, visible to everybody. So here we go:

Nr. one is a particular piece. Size is about 17x6x2 cm. You can see that it came from an irregular layer and would not qualify as the every-day coticule. I would even think that the unknowing honer would refuse to buy it.
I quickly passed an Eskilstuna over it and I would rate it as very hard and slow.

Nr. two is more towards the classical barber hone. It measures 16x3.4x1.3 cm, so it is actually a bit on the narrow side and will give me a hard time trying to guide my razors properly. It seem also quite hard but I did not pass any blade over it yet.

And last but not least here are the slurry test specimens.
From left to right we have Fast La Dressante, a La Veinette, and a Petite Blanche.

It is your turn now, Sir Bart.
Interesting. Bart sent me 3 slurries as well. Of particular note was the unmarked "raw" cut one. It looked like it was chipped off a rock and didn't look cut. The BBW on this stone is amazing. Ive tested 2 bbw's in my career, but this one's color blew me away! It should be called a BRW (belgian red whetstone). I will try and post pictures, the color is the deepest blood red I have ever seen in a slurry. It looks like red make-up with water in it. The coti side is red, green, purple, and yellow colored so it makes me think it is from a hybrid les latneuses. However, it has a BBW side on it, so who knows:confused:

Also, im finding that you can't change the speed in vast amounts by using a fast slurry stone. The slurry dulling affect can be controlled more though.

Example my hone is an unknown layer. here are its characteristics.
Speed with slurry (turns gray slowly, never gets black)
Speed on water (Fast: leaves black streaks on the hone in places)
Feedback (has a grating feeling of harsh abrasion)
Edge (leaves a brisker edge than my older barber special hone)

The slurries I rate like this
La veinette -Used this one medium times, slightly faster than normal, minimal slurry dulling
Mystery Raw rock - Use this one the most, noticable faster, more slurry dulling than veinette
La grosse (or was it petite?) blanch - Hardly used this one, between veinette and raw rock in speed, high slurry dulling effect.


The first Coticule is cut form a raw rock I collected at Tier du Mont.

Only yesterday, I commented about it in another thread.
Bart said:
The one you already have comes from the "Tier du Mont" area, which is about 2 km more to the East of the "Tier d'Ol Preu" quarry that Ardennes Coticule owns. I got it from one of several abandoned mining pits that can be found in that area. It's the same geological Coticule vein as Ol Preu, so based on the green color, I'd say that it's from the "La Verte" layer, though it behaves a bit differently than the La Vertes that I tested from Ol Preu.

It would qualify "slow" to "moderate" on the scale I use for estimating honing speed in the Vault. Keenness limit on slurry is ++/+++. Finish is "engaging" to "mellow".

Beware of using the other side. It has a huge quartz inclusion that would most likely seriously interfere with honing.

The second one is a very fast Coticule, unknown layer, unknown producer. (It's a vintage one) Keenness limit on slurry is +. Finish is "brisk".

Both stones are more or less on the far ends of the Coticule spectrum. They illustrate perfectly why differences between Coticules can't be qualified in terms of "better" and "best". The second one is faster, but that also makes it more challenging to use. But in the end, the edges will resemble each other closely.

Then the slurry stones, from left to right: La Dressante - La Veinette - La Petite Blanche.
I'm not going to comment on these, but Caleb made a few observations that make good sense to me. He has the other halves of your La Veinette and La Petite Blanche. (I 've cut them myself) His mystery slurry stone comes from a piece of raw Coticule that I picked up from a path in a forest at Joubiéval. It can't be used to cut hones, because it falls apart when cut. There are several Coticule layers that aren't commercially exploited for that reason. But small fragments can be used as slurry stone, or to sharpen larger knives. They're very fast. I understand the comparison with Les Latneuses, but it's most likely not from that Layer.

Kind regards,

Nah not showing off, thats for others, and alas not an offer either I am afraid, just a quick link to another thread, showing how useful a "Slurry" stone can be, I personally think that a slurry stone only has a slight effect on the finished honing job, but hey whatda I know .. lol

Best wishes
Yours Humbly
Ralfson (Dr)

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)
- Sharpness
- Finishing properties
- Surface appearance / scratch pattern (ok, that's more the techie approach …)

Basic considerations:
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"

Abrasion capability:
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?)

Experimental setup:
- 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)

Thanks for a most interesting read. However, I have some questions. Could it be that the slurry being built is primarily coming more from the larger coticule instead of the slurry stone? To test the potential difference, could you build a slurry with a DMT on the slurry stone and transfer it over and then compare it the slurry properties generated from rubbing the slurry stone on the coticule?

Does that even make sense to anyone?
I thought about that too.
That's's why I think it is so important that I had the very hard la Verte in the pool. Since this rock is so extremely hard I would assume that the slurry raised is almost exclusively made up by the slurry stone. Objections welcome.
Yet, no big difference did show on that one.

Here's a crazy thought I had. I wonder if a piece of glass or a flat stone with no grit of its own could be used for this experiment. That way, you could compare those results to the other two methods that were mentioned... might be fun to compare.
richmondesi said:
To test the potential difference, could you build a slurry with a DMT on the slurry stone and transfer it over and then compare it the slurry properties generated from rubbing the slurry stone on the coticule?

Does that even make sense to anyone?
I'm not convinced. In practical use, we are rubbing with the slurry stone over the hone, hence I think we don't need to test with a more complex procedure of slurry generation. If there are no significant differences with the normal technique, what would be the point of investigating a method no one is going to use. Unless we expect advantages that would lead to a new method.B)

I have tried slurry on glass. It works only for a brief moment. The garnets seem to quickly loose their bite.

Kind regards,

PS. I'm still busy with fully digesting Bluedun's excellent write-up. I will write a more thorough reply later.

I just noticed that I mixed upt x-stroke and half x-strokes!
In fact, what I did was half x-strokes with my finger on the blade and light pressure. So you can substitute "x-stroke" by "half x-stroke" anywhere in the post and in the pictures.

However, this does not change the generality of my observations.

Bart said:
richmondesi said:
I have tried slurry on glass. It works only for a brief moment. The garnets seem to quickly loose their bite.

Very interesting. I thought about that the whole day ....
You say the slurry looses its bite very quickly, i.e. the garnets in the slurry loose their cutting ability. That complies with my observation that the slurry stone does not change the speed of the coti significantly.
However, slurry does speed up a coti as oposed to pure water. From the above observations I conclude it cannot be the garnets in the slurry. Therefore it must be the matrix that is also finely ground and makes about 60 - 70 percent of a coti (if I recall correctly).

On the other hand a coti with slurry does not loose its cutting abilities but continues to shave off metal. We've seen that the slurry itself does not grind away the metal. Conclusion: The slurry helps to continuously release new garnets from the coti. And since the raw material composition of different cotis is quite similar (careful: Not HOW their physical structure is but what they are actually made of) the slurry produced by any of them (that's when the physical structure is gone) will behave very similar.
Or to take it to extreme I dare to postulate: If one could take a slurry stone and remove all the garnets but leave the rest, this slurry stone would still serve its purpose equally well!

Kinda theoretical, I know. But go ahead and try to prove me wrong :p

Bart said:
richmondesi said:
To test the potential difference, could you build a slurry with a DMT on the slurry stone and transfer it over and then compare it the slurry properties generated from rubbing the slurry stone on the coticule?

Does that even make sense to anyone?
I'm not convinced. In practical use, we are rubbing with the slurry stone over the hone, hence I think we don't need to test with a more complex procedure of slurry generation. If there are no significant differences with the normal technique, what would be the point of investigating a method no one is going to use. Unless we expect advantages that would lead to a new method.B)

I have tried slurry on glass. It works only for a brief moment. The garnets seem to quickly loose their bite.

Kind regards,

PS. I'm still busy with fully digesting Bluedun's excellent write-up. I will write a more thorough reply later.

Bart, I think having a 'baseline' of hone performance using slurry built up from a DMT or a slurry stone that's the same as the hone would be helpful. It would allow us to qualify what the effect of slurry from the slurry stone is vs. what the contribution from the slurry released by the hone itself is.

Practically, it would mean little unless the user had access to a slurry stone from the hone material (or could cut a bit of the hone off), assuming that the performance of the slurry from the hone itself exceeded that from the non-matching slurry stones.
First of all, a big formal thanks to Bluedun for devoting his time to this experiments.
:thumbup: :thumbup: :thumbup: :thumbup:

It is true, we are left with more questions than answers, but isn't that the starting point of all meaningful research, namely, the formulation of the right questions. I will briefly summarize them, and offer whatever insight I have on these matters.

1. the influence of the slurry stone on the speed of a Cotiule.
Bluedun formulated the question, and I believe he also answerred it. The influence is neglectible. I never ran the thorough kind of tests Bluedun performed, but I can confirm that the outcome doesn't surprise me at all, based on my own impressions with various slurry stones and Coticules.

I think the human factor is negligible. In essence, Bluedun rubbed steel over the hones withouh any concern about sharpness or resulting scratch patterns, evaluating only the color of the slurry. Any inconsistencies in the honing stroke wouldn't have mattered, except for pressure, but I'm sure our comrade is as capable maintaining pressure within certain limits as the next guy. Moreover, I firmly believe in experiment that are conducted in real life circumstances. Who cares that we might be able to measure differences in a lab situation with a robot doing perfect motions? After all, the question was if different slurry stones have an influence in a live honing practice.

I do wish to make one reservation, though. We musn't confuse slurry discoloration with abrasive speed. There are several factors that have an influence on the shade of the slurry, steel entering the mixture is only one of them. Hence ascribing speed differences to Coticules that only show different rates of slurry discoloration, however tempting, may not be entirely correct. Take Rutile for instance. Rutile is also known as Titanium Oxide. It is one of several phylosilicates that bind the garnets together, and it can be found in Colitcules in variable ratios. Rutile is a very opaque white mineral, used in paint, and a wide variety of white products, even in TicTacs. If you see a white object, Titanium Oxide is often nearby. There is little doubt that slurries with a lot of Rutile in it will tend to stay light gray, while slurry with little Rutile may become black at a rapid rate. Of course the amount of metal entering the mixture is of great influence as well. It's just not the only factor. Something to remember. (At present, the only variables for speed estimation I monitor while testing Coticules, are slurry discoloration and checking with the stereoscope how quickly a Coticule replaces scratches induced by my DMT-C. Both readings are only crude markers. Ralfson and I are working on a device that allows for a more precise speed measurement, but it's still a long shot). For Bluedun's slurry stones comparison, this is not all that important, because his direct comparisons are all made on a single specimen, but I still feel the point needs to be made. Bluedun tried if he could influence slurry discoloration by only altering one single factor: the slurry stone. Clearly it did not have any significant influence, hence the conclusion remains solid. Different slurry stones have no significant influence on the rate of steel entering the slurry. That can only mean they have no influence on the abrasion speed.

How comes? Why does the addition of garnets from a faster stone does not have a noticeable influence on the speed of a Coticule? Do we need to know? Do we even care? Probably not. It's unlikely someone will become better at razor sharpening by knowing the answer to that kind of question. But I love to formulate a good hypothesis before breakfast, as a matter of gymnastics for the mind. Here's what I came up with this morning:

When using a Coticule with slurry, it is only a very small portion of the slurry that simultaneously takes part in the actual abrasion. The bulk of the slurry just sits on top of the hone, traveling along while being "squeegeed" across the surface. Only the garnets that get caught between the bevel (or spine) and the surface are in a position to remove any steel. But how do they get caught in between? It is clear that on a matemathically flat and uninterrupted surface a mathematically flat an uninterupted bevel would either undercut all free floating matter or push it in front. But a bevel is never that perfect, so all kinds of particles will get trapped, including garnets. But the bevel isn't the sole responsible for that. Also the surface has numerous recesses in which garnets can spin as the bevel rides on top of them. I think that may be a very important factor: how good the constantly changing surface of the hone is at keeping the ganets trapped within cavities, firm enough to keep them in place, but loose enough to allow a fierce revolving. If the binding matrix is too fine and homogeneously structured, the cavities might be too shallow and sloping to grab the loose garnets in an efficient way. I can imagine how that can be a very important condition to enhance and unleash the true power of Spessartine garnets. And it would explain why adding garnets from a fast Coticule to a one that offers only a poor substrate for garnet action, would not yield much effect. All hypothetically speaking, of course.

Scientific research has been done about the composition of different Coticules. Differences were found between garnet content, average size of garnets and composition of the binder. Sadly, there is one obvious lacunae in all publications I have come across so far: none of the studies cared to first determine the sharpening qualities of the specimen they analysed. At best, they went along with the commercial "quality" of the compared specimens. a qualification that has been more inspired by marketing principles than by factual differences in honing properties.

2. The influence of the slurry stone on the "slurry-dulling" factor and its influence on the "dilution phase"
A double investigation, but probably so closely connected that both questions must be researched together. I disagree with Bluedun's reservations that he might lack the experience for that kind of research. For me, the dilution phase is all about reading the abrasiveness of the Coticule. That is a process I can control in a direct fashion. It really is like playing a musical instrument. Give a musical score to a novice and he will look at the first note, needs to look up in his memory what that note is, then he needs to look up in his memory what finger setting that note correlates with on his instrument, and finally he can put his untrained motor skills into action to actually play that note. By that time the orkest has already finished the second bar. A seasoned player, on the other hand, sees the notes and his body plays them, just like we can read words and our mouth speaks them, without the need to remember what the characters mean and how they need to be pronounced. Honing on a Coticule is the same for me and all others experienced on these whetstones. We don't consciously monitor all the elements that the apprentice has no choise about but to occupy himself with. We just make the razor sharp. My sincere apologies for the pretentious connotation of that statement, but that's just how it is. Asking me to address the differences of slurry stones on the honing process, is like asking a guitarplayer whether a G-chord is easier to grab than a D-chord. A novice player might have a meaningful anwer and perhaps even a few tips, but a developed player probably won't remember.
I think it is key for this experiment that a less experienced Coticule user tries to succesfully perform Dilucot with the various combinations of Coticules and slurry stones. If there are combinations that make it easier to reach good results, I'm sure that will show up. After conclusion, we can send the package to the next in line and find out if he has a similar experience. I think the only requirement is a sound honing stroke, which is a conditio sine qua non for all razor honing. Anyone who can reach a good edge with Unicot and/or a progressive approach with a "middle hone", is ready to learn Dilucot, should he be interested in mastering it. I have always figured that Coticules with less "slurry-dulling" were easier to start out, but not everyone seems to agree. I specifically selected one with "+" for slurry-limit (the vintage one) and one with "++/+++" (the La Verte). And there the La Veinette slurry stone, a layer I always had the impression that it was "easy-going'. But as said, the more I learn about Coticules, the less likely I am to restate that sort of claims.

I hope at least someone read this far.:-/

Kind regards,
I read it Bart... Makes sense to me. I can't relate to the music analogy, but many other similar things came to mind.