1930s Czech Folded and Textured Black Pressed Glass Bow Brooch

Very pretty vintage black glass brooch in the shape of a folded and textured bow.
Probably from the 1930s but maybe older.
It's 6cm long, 1.5cm wide and has a slightly rusty pin - easily cleaned up.
CZECHOSLOVAKIA  printed on their display cards.
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)