Antique ruby and diamond half hoop ring, featuring Burma rubies

The central oval facetted ruby between old European cut diamonds, two smaller rubies to either side and diamond line shoulders to the half hoop, open set in gold and with platinum to the diamonds settings, stamped '18CT PLAT', accompanied by GPL report no. 19749 for the rubies giving a Burma origin opinion and that they show no evidence of heat treatment.
Width maximum at head 8mm
Length half hoop 21mm
Weight: 5.5g