I've got one of the Ardennes La Pyrenees (Saurat) / BBW combo stones. This has been my experience with it...
The stone is advertised at ~1200 grit aggression, which makes one imagine it's a medium-grit natural stone, like a Binsui, Washita, etc. However, like the Finnish Wastikivi, it's actually just a fairly clean, surprisingly fine/slow-cutting piece of schist/slate that's been surfaced with deep, linear grooves that help it to act like a file. If you ever make the mistake of lapping one, you'll quickly discover that these aren't mid-grit stones by nature, but more by surface treatment.
The Ardennes La Pyrenees/Saurat stones (With their factory grooves.) cut best by drawing the knife across the stone in a single sweep, just as one would with a honing steel. This can remove metal more quickly than a normal fine stone, but it doesn't
feel like how a medium-grit natural stone normally does. It's just sort of a stone file. The edges tend to be ragged with the factory lapping, though on the right steel, with lengthy experimentation, a very toothy and keen edge can be achieved... Unfortunately, since these stones aren't even vaguely flat, this can be a frustrating, and difficult to repeat experience out of the box. Again, everything I write also applies to the Wastikivi.
It works best on simpler/low-wear-resistance knives... 10xx, or maybe 12C27/420HC in the 50's HRC. The coarse factory lapping tears up the edge of a hard, Shirogami blade, and is not effective on anything with any volume of harder carbides.
If you wear the lapped grooves on such a stone down with sharpening, or make the mistake of lapping it yourself, it will no longer be something masquerading as a mid-grit stone. After I lapped my La Pyrenees/Saurat on an Atoma 140 when I got fed up with its lack of flatness, it became a very slow/ineffective finishing stone that cut infinitely more slowly, and left a - surprisingly - slightly finer, though very bland edge than the BBW strapped to other side of it. Honestly, it just feels like sharpening on a random piece of found slate if you've worn or erased the factory surfacing.
I've since tried resurfacing it with loose 80-grit SiC, and this still isn't anywhere near enough to replicate the factory surface finish. I think you'd have to use at least 24-grit, or coarser. It's a pretty extreme texture that's needed to make such a stone ape a mid-grit.
I have found two videos on the manufacture of these stones, for anyone who is interested:
Pierre a aiguiser naturelle des Pyrénées
Le dernier fabricant de pierre à aiguiser de France - Météo à la carte
These were an interesting adventure into sharpening stones, but not one I would repeat.
Hope this helps.
) , but it's where the real power of these stones reside.
(I just need to learn to read)
