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Hi Sophie.
What a strange world...! On Sunday, a Belgian couple showed me images of their collection, which included a paperweight containing what is, I think, the same sulphide as the one on eBay. Theirs was not coloured, but I am fairly sure it is the same sulphide as the one on eBay - we discussed the differences between their example and the one Paul Ysart used. They were fairly sure that their example was a Belgian or Alsace piece.
The white spatter ground of the one on eBay also suggests to me that Belgium or Alsace is the origin.
Alan