Antique Bronze Intaglio with Amethyst?

Hello everyone! I have recently acquired an intaglio ring. To me the metal looks like bronze, perhaps it was gold cased at some point - I can see some faint marks on the inside but these might as well just be dents. It has pretty leaves and what looks like vines. As for the stone, it could be glass or an amethyst? It has no visible inclusions inside. I haven't found a similar ring online, so I would love to know any information anyone might have about it

 

Glass & base metal of some sort, originally made to look like gold.

 

Probably brass. Quite common in the late nineteenth and early twentieth which is when I suspect this was made.