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Then this is the darkest BBW I have ever seen! I once heard of grey BBW, though. Very nice indeed. You definetely have a naturally grown BBW Coti combo. Enjoy it :y

You are able to see garnets? At what magnification, as they linger around 6-20µm.

There is a very easy to clarify if it´s a natural combo with bbw, or natural combo with schist (both exist).
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I can´t see a BBW there :thinking:

yes, it is much more evident now. It´s clearly a natural.
Unfortunately it seems to be grown to schist* that is (almost) unusable for sharpening action.
But the stone is extremely nice anyway!

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Oh, well I stand corrected then :w

And it was my bad with the natural/artificial confusion, too.
I missed the point.
I don´t think there is a difference in the look and appearance of the border.

This of course depends. Genrally spoken, yes there is a difference in value.
A naturally grown combo stone is far more rare than an artificial one.
Anybodoy can glue a coticule to a bbw.
So given...

Yes, there is a difference. If the line between Coti and BBW is very sharp,
it is possible that the BBW has been glued to the Coti.
So it is an artificial combo, but not a natural.
A natural...

I would like to contribute my coticule as well, because I enjoyed it recently. I get shaves off of it (without further refinement) that easily compare to my Maruka Nakayama Kiita and vintage...