Nice looking inserts. Cut rim + engraving points towards Czech or the German / Czech border regions for the glass, which looks
good quality ....what's your estimation ?
Of course the metal work could well be made in a different country in any case.
but I don't think these are German they have a ‘bell époque’ with whiplash look about them.
So does much early WMF ! and so does some of the output of Orvit and Kayserzin (spell ?) (Edit Correction : Kayserzinn) which were both taken over by WMF I believe.
One if not both of these were in Belgium or near there I think.
Another possible maker is Urania in Maastricht ...and if I have this right, their work was marked "Imperial-Zinn".
Here's a book ref
Art Nouveau Domestic Metalwork: From Wurttembergische Metallwaren Fabrik 1906, 2nd Edition
Antique Collectors Club, Wurttembergische Metallwarenfabrik, Graham Dry
Hardcover / 389 Pages / Antique Collectors Club Ltd / March 2006
and a website for marks http://www.antikonline.de/wmfmarks1.htm
I will also write to a very knowledgable collector to ask for his input here.