Today, most of us use coticules as finishing hones, without raising a slurry. Unless a stone has inclusions of coarse and hard foreign deposits, they all perform within a fairly close range. The "Ardennes Coticule" quarry does not produce hones from raw rocks with such defects.
In the old days, people used coticules for tasks we nowadays usually perform with coarser synthetic hones such as those produced by Norton and DMT. Speed was a major factor for assessing quality. Coticule is extracted out of the undergound of a rather small area in the Ardennes region in Belgium. There are a few main veins that each consist of several layers. The layers all have their own capabilities, and even within a layer, there are differences. Some layers were not used for the production of hones, in the old days, because the raw coticule they contain is too slow for anything more than polishing. Some veins were "richer" on good coticule than others. The most reputed mines had access to the most reputed veins.
"Ardennes Coticule" is quarrying former mining pits, rescueing raw coticule that was too difficult to extract with the old mining methods. I can only assume that they also exploit layers that in the old days were cosidered inferior due to the aforementioned lack of speed. I have seen coticules that were avid finishers, but by any means too slow for serious steel removal.
When I visited the quarry a few months ago, they had recently hit the bottom of the former mining pits. This opens perspectives for extracting coticule from previously untouched layers. Rob Celis from Ardennes Coticule said they hoped for bigger pieces of rock, because of the high demand of rectangular bigger sized hones. At the moment, they have plenty of irregularly shaped "bouts", but low supply of larger hones. I also assume that we might see more of the "fast" layers in the future. Ardennes Coticule also owns a second mine, with access to formerly renowned layers, but the investment for exploiting that mine in compliance with modern safety standards is too big to be a priority, according to Rob Celis.
I have two lightning fast coticules, one is a vintage hone, the other recently purchased from Ardennes. The vintage one is so soft that it creates slurry just from honing. A property that makes it my worst finisher, 'cause loose coticule garnets have a bit of a blunting effect on the very edge of a razor. The recent coticule does not display this disadvantage, but it leaves visually (under magnification) the coarsest scratch pattern of them all. As stated before, with exception of that vintage one, they are all more than decent finishers, with only very minor differences in the final results.
If you're intrested in seeying some picture, with the full story of my visit at the quarry:
http://straightrazorpalace.com/advan...ticule+diaries
http://straightrazorpalace.com/advan...ticule+diaries
Best regards,
Bart.