A late 19th century diamond tiara

A late 19th century diamond tiara, converting to a necklace, probably French, set with graduated cushion-shaped diamonds in cut-down collets, further trefoils of old circular-cut diamonds, old cushion-shaped diamonds in square-shaped collets and a lower row of rose-cut diamonds, all in silver on gold, the diamond section detaches from the tiara frame to be worn as a necklace with a detachable diamond-set backchain, French control marks to back chain, 3cm high (as a tiara, including frame), 38cm long (as a necklace), fitted case