Homura's Soul Gem from Puella Magi Madoka Magica
This is the base of Homura's soul gem. I modeled it after the original concept art.
This was originally intended for cosplay, since I couldn't find any Homura soul gem that was exactly accurate to the anime design.
I do wish that the edge could be thinner, but according to stainless steel design guidelines the base must be 3mm thick.
You can print this in plastic to cast with resin and gold powder too--I think it would work just as well!