A collection of opal and diamond jewels, early 20th century

A collection of opal and diamond jewels, early 20th century, comprising: an opal and diamond bar brooch, mounted in gold, length 4.4cm; a ring set with three black opals, spaced with circular-cut diamonds, mounted in gold, size M, a bar brooch centring on a pearl within a border of circular-cut diamonds, mounted in gold, length 3.9cm, pearl untested; and a diamond ring set with three brilliant-cut diamonds, mounted in gold and platinum, size M1/2, stamped 18CT PLAT