So I've done some sleuthing already and I have determined that my ring is a gorgeous 1930's antique engagement ring! Inside it has a PAT# 2016492 which I have researched to be a design by Joseph Granat. However there is another stamp inside that seems to be "GMCD" or maybe "GMCo" (see photo). I cannot find information linking Granat to this stamp so I am wondering if he may have allowed other manufacturers to use his patent? I also can't seem to find who the GMCD stamp belongs to. I would really love to find an antique wedding band that matches/pairs well with my ring but I am considering taking the drawings from the patent to a jeweler to have one designed for me.
The patent BTW can be found here: https://www.google.com/patents/US2016492





The patent BTW can be found here: https://www.google.com/patents/US2016492




