If the stone is 40 years old, than I am fairly positive that it will have a bbw backing, IF it is a coti. It looks like one, but I have seen some synth combination stones that looked deceivingly like cotis.
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It does look like a Coticule. Most old Coti's were backed with BBW's. Yours is a tough call from the pics. Try wetting the blue side, and rubbing it with some wet sandpaper. If you get a purple slurry mixture, then it's a BBW for sure. Even just wetting it sometimes, you can see the stone is purple and spotted, rather than black....
The yellow side will also probduce slurry about the same color as the stone if it's a Coti.
Take a look at the second item in this on line catalogue: http://www.kirschen.de/_pdf/katalog2...lehrmittel.pdf
They sell 3 sizes, the number six is 115x60 mm. Would that be the size of your stone?
I have been told it is a natural sharpening stone, coarser than the coticule.
That's a great catalogue, Kees - thanks for posting it. I like that grinder with four wheels on it...!
There is an american version of the Two Cherries catalogue that has this on it:
Attachment 99801
Regards,
Neil
@Neil
you may like their German/English Catalogue. I quickly browsed thru it, it looks like it has even more items in it: http://www.kirschen.de/_pdf/katalog2...log_gesamt.pdf
It fooled me well. But Coti does not drink.