Larger Particles In This Coticule?

[lightfoot]

Here’s a close-up of a Coticule that’s given me lots of grief over the years.

If you look you can see this frosty white hue across the surface of the stone and I’m assuming these are likely the very very fine garnets but what are these larger forms imbedded in the stone? Are these larger garnets or something else?

 

[lightfoot]

While I can clearly see the crystal-like garnets in person they can’t be seen in the photos practically speaking…

 

[kcb5150]

I think it may just be material orientation. Sort of like the jnat squiggles that can spit bigger bits into the water. It looks like some lobes of stone are sort of parallel to the honing surface and maybe along the edges they occasionally spit up material.

 

[iamryan25]

I found this description in the 2016 Coticule study by Alain Herbosch (Coticules of the Belgian type area (Stavelot-Venn Massif): Limy turbidites within the nascent Rheic oceanic basin).

"[T]he coticules of types 1, 2 and 3 can bear yellow, white or reddish andalusite/kaolinite spots in their spessartine-rich layer units" (p. 197).

I believe these are the spots we see in many yellow coticules. (The spots that aren't manganese).

I see them mistaken for garnets. However, they're larger than the microscopic spessartine garnets. Garnets in coticules are about the same size as a red blood cell. So we can't see them easily, even with magnification.

 

[lightfoot]

I found this description in the 2016 Coticule study by Alain Herbosch (Coticules of the Belgian type area (Stavelot-Venn Massif): Limy turbidites within the nascent Rheic oceanic basin).

"[T]he coticules of types 1, 2 and 3 can bear yellow, white or reddish andalusite/kaolinite spots in their spessartine-rich layer units" (p. 197).

I believe these are the spots we see in many yellow coticules. (The spots that aren't manganese).

I see them mistaken for garnets. However, they're larger than the microscopic spessartine garnets. Garnets in coticules are about the same size as a red blood cell. So we can't see them easily, even with magnification.

Yes, this sounds like this is what I’m seeing. The abrasives garnets offer a hint of sparkle if the stone is angled just right so they’re definitely too small to see with basic magnification.

 

[lightfoot]

I think it may just be material orientation. Sort of like the jnat squiggles that can spit bigger bits into the water. It looks like some lobes of stone are sort of parallel to the honing surface and maybe along the edges they occasionally spit up material.

I’m wording all of this very badly….

The features that I am really uncertain about are the tiny little yellow shapes not the frosty swirls. You can see these especially clear in the first two photos but the last photo doesn’t offer a very clear view unfortunately.

I guess my question is whether or not this material is inert or abrasive.

 

[Darth Scandalous]

What's the magnification in your photos?

 

[lightfoot]

What's the magnification in your photos?

Not sure. It’s a combination of a 10X loupe and photo enlargement.

The particles are easy enough to see though. They have sort of a rounded shape and the Hue is roughly a yellow ocher.

The following image is the best I can do. I’ve altered the contrast a little bit.

 

[Gamma]

A lot of what many people see reflecting light in a Coticule is mica.

Coticules are known to contain garnets with a broad range of particle sizes.
Because the garnets are embedded, and the entire crystal doesn't stick out, the actual size of the garnets might be misleading to someone trying to gauge grit vs particle size.
Making slurry opens a new chapter though... now the garnets are rolling about loose. People doing circles, with any pressure, on a stone with any number larger than average garnets, can run into trouble finishing on slurry.
Auto slurrying stones can cause issues here too.
This is one reason why technique is a key element with using Coticules, they are not 'add water and stir' stones.

 

[lightfoot]

A lot of what many people see reflecting light in a Coticule is mica.

Coticules are known to contain garnets with a broad range of particle sizes.
Because the garnets are embedded, and the entire crystal doesn't stick out, the actual size of the garnets might be misleading to someone trying to gauge grit vs particle size.
Making slurry opens a new chapter though... now the garnets are rolling about loose. People doing circles, with any pressure, on a stone with any number larger than average garnets, can run into trouble finishing on slurry.
Auto slurrying stones can cause issues here too.
This is one reason why technique is a key element with using Coticules, they are not 'add water and stir' stones.

Seems like the surrounding material is going to factor in as well.

I have a couple that are very very fine and uniform in appearance under magnification. They almost look like a synthetic stone at a passing glance in fact. These also have these semi-ovaled features in them as well but the surrounding material looks more similar in density as far as I can tell where as some of the examples that have that granular appearance have a much more varied topography and often have less fine results on the edge.

No hard and fast determinations can be made by examining the surface texture though but it’s extremely engaging none the less.

 

[Gamma]

The entire stone matters. That's why auto slurrying stones are more difficult to finish on. If the matrix is soft and loose slurry is preventing edge development, technique has to take over.

I've had a boat load of Las Petas that looked like that and were phenomenal. Some had feedback that felt like honing on marbles.
I have had La Grise with that surface texture and they would challenge me to finish on them.

I don't spend time trying to determine what the visual means because I don't think it matters. Over the years many many assumptions have been made, which resulted in labels being put on stones, and a lot of it is just false positives, one-offs, or circumstantial.

The bulk of my time is invested in sensing the feedback and checking the edge performance.
Sometimes they're just puzzles pretending to be a rock.

 

[SliceOfLife]

My best guess from what I've seen looking at stones surface and slurrying and seeing what is let loose under a scope is that those big blobs are possibly stone material aggregating and binding (resisting lapping/usage) around objects; often garnets or clusters of garnets under the surface; but are not garnets themselves. As gamma notes; seeing stuff like that doesn't always mean there's big ol honkin garnets in the stone; but sometimes it does. Frankly zoomed in photos of coticules surface is, in my experience, less useful at judging a stones character than just looking at the stone without magnification... just because certain markers (basically the same ones that make stones pretty/desirable/expensive) most of the time are at least SOMEWHAT reliable in predicting the stone's behavior... whereas there's a lot less breadth of knowledge/testing done after looking at stones zoomed in like you have.


But generally, from your pictures, I'd assume this coti looks slightly flakey or scaley or shimmery without the mag... and those are usually stones I'm not partial to... a few Modern/Ardennes stones I've tried were like that and they ranged from avg to below avg. So I typically avoid that kind of fish-scale look on coticules.

 

[bmiller3230]

That looks like my best La Grise. It's excellent at finishing, but needs a fast slurry stone for low and mid-range work. It does provide a very keen and smooth finished edge, though

 

[lightfoot]

After revisiting this stone it’s pretty obvious as to what’s going on. The stone’s too soft and sheds like there’s no tomorrow!

The top-end of the stone is limited even under running water. The softness of the stone’s just a limiting factor but it does a really nice job clearing 1K/2k synthetic work. It leaves an even scratch pattern and sets the edge up well for a finer stone. But the softness just won’t let the apex get thin enough for shaving by itself.

Still a good stone for what it can do though.

 

[iamryan25]

After revisiting this stone it’s pretty obvious as to what’s going on. The stone’s too soft and sheds like there’s no tomorrow!

The top-end of the stone is limited even under running water. The softness of the stone’s just a limiting factor but it does a really nice job clearing 1K/2k synthetic work. It leaves an even scratch pattern and sets the edge up well for a finer stone. But the softness just won’t let the apex get thin enough for shaving by itself.

Still a good stone for what it can do though.

Try finishing with oil after a synthetic 8k to add glide and reduce self-slurry. These were historically sold as oil stones. Coticules aren't porous and can safely switch from water to oil to water (a little dish soap makes cleanup easier).

 

[lightfoot]

Try finishing with oil after a synthetic 8k to add glide and reduce self-slurry. These were historically sold as oil stones. Coticules aren't porous and can safely switch from water to oil to water (a little dish soap makes cleanup easier).

I appreciate the suggestion and it may in fact help someone out there to get some use out of another stone but I’ve tried all that stuff a million times on this one.

What I had failed to notice earlier in my attempts with the stone is how much the stone would auto-slurry.

I’ve tried both oil and lather and it does in fact cut down on the phenomenon but only to an extent.

The truth is that I don’t need the stone to be something that it fundamentally isn’t. Figuring out a stone could involve finding a work-around for a challenging stone and it also means accepting a stone’s limitations as well.

I’m completely at peace with what the stone can do as well as it’s limits.

 

[Gamma]

Oil on an auto-slurrying stone only reduces some friction, it doesn't really stop the stone from releasing particulate. If the auto slurrying is bad, oil can make things worse by allowing clumping. Usually not the case though.
Adjusting pressure correctly will eliminate the need for a lube, it does the same thing. If a super light touch is not available, then a lube can fill in the gaps.

The only way I found to quasi-defeat the auto-slurry issue is to hone uphill under drizzling water - it's a gravity-assist move. Done correctly the water flushes a lot of the problem away. It's not an absolute work around but it will help achieve a finer apex.

I'd rather not wrestle with a stone though, but sometimes there is no option.

 

[Empire straights]

I appreciate the suggestion and it may in fact help someone out there to get some use out of another stone but I’ve tried all that stuff a million times on this one.

What I had failed to notice earlier in my attempts with the stone is how much the stone would auto-slurry.

I’ve tried both oil and lather and it does in fact cut down on the phenomenon but only to an extent.

The truth is that I don’t need the stone to be something that it fundamentally isn’t. Figuring out a stone could involve finding a work-around for a challenging stone and it also means accepting a stone’s limitations as well.

I’m completely at peace with what the stone can do as well as it’s limits.

One thing I can say about those softer coticules that auto slurry.... they may not be the pick for a finishing stone, but they are usually blazing fast for your low-mid range work and can be very useful to have around. I didn't give my soft la gris to my son until I got a hard vintage coticule that's fairly coarse for a coticule(about 6k) and actually leaves teeth on a knife edge. I use coticules for all kinds of edged tools so having a coarser one that's really fast was a win to me. When looking for finishing coticules I personally have had much better luck with the old ones but all of them are useful. Those garnets very quickly cut any type of steel I've put to them my Cresent 5cr15mov work knife will tune up quickly on one and it's really hard steel that holds an edge forever, even with tons of use.

 

[lightfoot]

One thing I can say about those softer coticules that auto slurry.... they may not be the pick for a finishing stone, but they are usually blazing fast for your low-mid range work and can be very useful to have around. I didn't give my soft la gris to my son until I got a hard vintage coticule that's fairly coarse for a coticule(about 6k) and actually leaves teeth on a knife edge. I use coticules for all kinds of edged tools so having a coarser one that's really fast was a win to me. When looking for finishing coticules I personally have had much better luck with the old ones but all of them are useful. Those garnets very quickly cut any type of steel I've put to them my Cresent 5cr15mov work knife will tune up quickly on one and it's really hard steel that holds an edge forever, even with tons of use.

When it comes to finding a stone suitable for razor finishing I think reaching out to the seller and sharing one’s expectations. It’s helpful to share the setup that one has in mind with the vendor as well.

I’ve never shared my expectations with a seller before and as a consequence I have a mixed bag of Coticules that are all over the place.

Next time I’m starting a dialogue with the chosen seller. I’m interested to see if that’s a more productive approach.