Vintage 12 Kt Gold Filled Carved Shell Cameo Screw Back Earrings Marked

Beautiful pair of vintage 12 kt gold filled shell cameo screwback earrings. Long oval shaped with pretty border frame work. Stamped on back screw knob 1/20 - 12 KT GOLD FILLED. Also appears to have a maker's mark, but I can't make it out. They measure approximately 0.6" long. In very good pre-owned condition. One screwback mechanism slightly curves downward, but does not interfere with use.