Thank you Paul! Yes, I have flicked it and it has a ring, not as nice as with thinner lead glass, but also not as dull as it is usually with non-lead glass, so I am not sure what the material is. Maybe it is safer to assume that it is not lead-glass... The ribs can be felt on the inside also. You are right, the cornflower was regarded in Germany as the "Prussian flower", it was the favourite flower of the king of Prussia and later Emperor Wilhelm I. and in memory of his childhood. However, in the romantic movement in Germany the "blaue Blume", the "blue flower", was also a central symbol. So maybe it could be German in the end? There are some German makers that also used these vivid enamel colours, like Theresienthal?