Thread: Belgian coticule, clarifications

Originally Posted by Bill S

I was under the impression that the Belgian Blue and the Coticule differed in the concentration of the garnets rather than their shape. Don't the garnets change shape as they are cleaved during honing?

I don't believe we can cleave the micro-crystalline garnets while honing.

And you are right the Yellow Coticule has 35% - 43% garnets,
the Belgian Blue has 30 % garnets.

But the important difference is garnets shape:
Yellow Coticule is more abrasive, it’s a better sharpening stone...
the Belgian Blue more a polishing stone.

Originally Posted by Carioca

I don't believe we can cleave the micro-crystalline garnets while honing.

And you are right the Yellow Coticule has 35% - 43% garnets,
the Belgian Blue has 30 % garnets.

But the important difference is garnets shape:
Yellow Coticule is more abrasive, it’s a better sharpening stone...
the Belgian Blue more a polishing stone.

Interesting conclusions. One of our members, Bart, has experimented with coticules and blues extensively. Here is a thread from the archives where he draws his conclusions. In addition to Bart there is a post in the thread from Howard, another SRP member with extensive experience with many natural and man made stones and their use. I think you would find the thread interesting.

I am new to the Yellow Coticule but it has changed the way that I look at honing. I have not honed a huge amount of razors but what I like about it is the feedback. The sounds and the feel on a Coticule will basically tell you when you have had enough strokes. With a slurry you can not over hone and with only water it is a pretty fine polisher. I then go to a 16K, then the pastes. I need a razor that is very sharp because with my beard it can be very frustrating to get a good shave sometimes if it is not.

Like so many things about shaving and honing it can be a very hard to make generalities that work for everyone. I will say that for someone that has been only into straights for a short time, less than 2 years, the Coticule has added a dimension to honing that has really made it a pleasure to hone. Finally my razors are very sharp and more importantly very smooth.

Take Care,
Richard

Originally Posted by JimmyHAD

Welcome to SRP ! Nice to have a new member who comes with some fore knowledge of hones.

Thank you!

Originally Posted by JimmyHAD

I am under the impression that those numbers are rough estimates when it comes to coticules and other natural stones ?

There are not only rough estimations, I remember that in 1996/1997 the new proprietor of the Old Stock, a coticule quarry, had geological analysis in University of Liège... And also I remember scanning-electron-micrograph-photos...

Found :

http://www.ellida.at/bb/B_Brocken_gelb.jpg
http://www.ellida.at/bb/Analyse.jpg

Originally Posted by JimmyHAD

Anyhow, on some razors I like to use the blue/yellow after I set the bevel with a DMT 1200 or a Shapton 1K. I have fooled with setting a bevel with various coticules with slurry and it can be done but for me it takes too long. Especially if you have a good alternative such as those listed above.

So do I. First a 1200 synthetic hone, than a Yellow Coticule, than a Belgian Blue.

Originally Posted by JimmyHAD

I like coticules for finishing but I get an even smoother edge (to my face) with the Blue/green or yellow/green Escher.

I never finish with Belgian Blue or Yellow Stone (both with garnets = Mohs scale of mineral hardness 8) - I always finish with a Thuringian stone or since some months with the BM-Schiefer (both with quartz = Mohs scale of mineral hardness 7) – that’s my icing on the cake!

Originally Posted by JimmyHAD

I like coticules because of the history, the romance and mystique of the hones. I think it is cool to use a natural stone rather than man made. OTOH I dig my man made hones and use them plenty too. Depends on the razor. As far as numbers go shaving off a razor finished on a coticule feels to me about like shaving with one finished off of a Norton 8k only smoother. An Escher gives it more smoothness (talking shave here). YMMV.

I dont like them... I love them, I inherit one Yellow Coticule from my grandpa and we live 80 kilometres from the Ardennes, so no mystique here ! For me they are very normal, I just love them for the efficiency and... the smell.

But when it comes to finish, natural stones are simply the best!

Originally Posted by Carioca

I dont like them... I love them, I inherit one Yellow Coticule from my grandpa and we live 80 kilometres from the Ardennes, so no mystique here ! For me they are very normal, I just love them for the efficiency and... the smell.

But when it comes to finish, natural stones are simply the best!

Obviously you have considerable experience with the coticule and other stones. Bart is in Belgium too and has posted on visiting the Ardennes quarry here and here. Perhaps you two will be fast friends and maybe collaborators on our passion.

Originally Posted by JimmyHAD

Obviously you have considerable experience with the coticule and other stones. Bart is in Belgium too and has posted on visiting the Ardennes quarry here and here. Perhaps you two will be fast friends and maybe collaborators on our passion.

I'm in Germany. Right between Ardennes and Solingen

Jimmy, thank you for the links

Originally Posted by Carioca

I never finish with Belgian Blue or Yellow Stone (both with garnets = Mohs scale of mineral hardness 8) - I always finish with a Thuringian stone or since some months with the BM-Schiefer (both with quartz = Mohs scale of mineral hardness 7) – that’s my icing on the cake!

+1 I have come to the same conclusion and routine when I use the coticule and Escher.

Originally Posted by JimmyHAD

+1 I have come to the same conclusion and routine when I use the coticule and Escher.

Jimmy, thank you for the links!

I'm in Germany, right between Ardennes and Solingen.

Originally Posted by Carioca

Jimmy, thank you for the links!

I'm in Germany, right between Ardennes and Solingen.

Here are two more you will enjoy. This one addresses the question of there being a progression in Thuringans based on color. The question arising from Escher Co, labeling their stones by color.Also another great coticule thread from Rob at Ardennes here.

Originally Posted by Carioca

"Football-like" (rhombic dodecahedron) garnets are in the Belgian Blue Stone!

In the (Yellow) Coticule the garnet-crystals are crumbled and more polymorphic. That’s also the reason why the blue and the yellow stone differ in grit:

Belgian Blue Stone is a 5000 - 6000 grit and the
Yellow Coticule is an 6000 - 8000 grit.

Hi Carioca,
Great to see a guy with Coticule and BBW knowlegde boarding SRP. Welcome!

I carry a special interest in the Belgian hones, and have been reading everything about them that I can get my hands on. There not only being a difference in average garnet size between Coticules and BBW's, is something I already read at different sources, but there also being a significant difference in shape is completely new information for me. Thanks for sharing.
The most up to date information I have, is in the excellent book "Ardoise et Coticule en Terre de Salm" (Slate and Coticule in the Salm Region), published in 2008 by the Geological Department of the Belgian Royal Institute for Natural Science. The charpter about the chemical composition of Coticule-stone and it's blue nephew, written by Prof. Eric Goemaere, is the most comprehensive text I have read so far, but he doen't mention shape differences other than size, between the garnets found in Coticule and those found in the Blue Schist.
According to Goemaere, Coticules are for more than 95% composed of three main ingredients: Spessartine Garnets, Phyllosilates (muscovite, paragonite, chlorite and kaolinite), and Quartz. The pyllosilicates have a hardness of 2-3 on the Mohs scale, hence they take no direct part in the abrasive process. Garnets and Quartz are 7 on the Mohs scale. Quarts is extremely finely grained in Coticules, it takes only part in the release of fresh Garnets during honing. The main contribution to the stones honing abilities comes largely from the garnets.
Fe²O³, which is responisble for the typical color of Blue Whestone, is almost absent in Coticule. The rest of the composing elements are almost the same in BBW as in Coticule, albeit they are present in different ratios. According to Goemaere, the garnets in the Blue are significantly larger, up to 30 micron. There's much more in the book, too much to get into in this post. The ISBN n° is: 978-2-9600676-1-3, written in French.

On a more personal level, I prefer an edge finished on a Coticule with water (thus with the garnets embedded in the surface of the hone), over an edge finished on the BBW with water or slurry.
With water, the BBW seems to dull the edge, rather than sharpening it. I have noticed the same on marble and other surfaces I ran a few experiments on. I speculate that any rubbing of an edge over a surface is going to be slightly detrimental to the tip of that edge, hence a dulling effect.
If the surface in question has sufficient abrasive qualilties, there will be enough material removed off the bevel faces to have a sharpening effect. If the sharpening effect is greater than the dulling effect, the edge can benefit.
What little tests I have done on the Blue with only water, seemed to support that hypothesis in a way that the edge lost keenness. On the Blue with slurry, the edge gained keenness till a certain level, where it maxed out, whitout any adverse affect of doing more honing, but without any improvement either.
It seems to me that the Coticule with water is still abrasive enough to improve, or at least polish the edge without dulling it.

I dislike rating the Belgian hones with a grit rating, because the versatility of their various ways of use, and because such rating is in contradiction with the actual size of the garnets and even with the visual appearance of the scratch pattern they leave. Rajagra shared a great picture in that respect.

Best regards,

Bart.