Hi Ken, I think Christine means the bottom side of the base, as Inwald is known especially for highly polished shiny (mirror-finish) bases on many of their items, so that can be a good pointer towards their output.
It's a fascinating piece and I've never seen one like this before... I'd have assumed American rather than European without the
Made in Czechoslovakia mark.
There's nothing like it shown in
Schránky Vůnà - České toaletnà sklo od počátků do současnosti by Jitka Lněničková, Petr Nový a kol., (published Jablonec nad Nisou 1999).
Hopefully someone will be able to help with more information. :thup: