If yours is a YG Escher, than a stone I have with no inclusions that's actually bonded to a handmade wooden razor box is also a YG Escher?.
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My stone looks identical to one of your first pictures. Mine is quite thin at about 3/8" but same color variation. The strop that's part of this vintage kit I describe is either true russian shell (diamond pattern embossed on the back or a vintage clever imitation).

The stone in the above pic is absolutely silky smooth and does not lap easily.

Chris L