Lively 1930s Deco Pressed Black Glass Floral Brooch

A striking Deco design on this black pressed glass brooch.
Probably from the 1930s but maybe older.
It's an impressive 9cm long, 1.5cm wide.
The underside edges are slightly rough with a couple of nicks, but could have been caused during manufacture rather than subsequently - don't notice on the surface.
I just have 1.
Other similar ones I have sold had CZECHOSLOVAKIA impressed on the back.
Czechoslovakia was formed in 1918  but the region of Bohemia and the Czech lands had been famous for glass production for hundreds of years (stating in the 1500s)