I've found this old abused and neglected whetstone in storage that belonged to my grandfather. Apparently he used it for sharpening kitchen knives but I do know that he shaved with a straight razor. It might be a Belgian Coticule.

The one side is this off yellow (spots where its not filthy) and extremely smooth and the other side is this coarse grey material. Like I said , it's really filthy as if particles from the grey side oozed all over the yellow side.

How do I clean this thing and how can I find out if it's a Belgian Coticule or not ? My grandfather never purchased crap :P