A rock crystal and enamel 'Stuart Crystal' mourning ring, circa 1766, centring on a step-cut rock

A rock crystal and enamel 'Stuart Crystal' mourning ring, circa 1766, centring on a step-cut rock crystal in a closed setting enclosing hairwork forming the initials WS, to openwork foliate shoulders and a band applied with black enamel, the commemorative inscription 'W STUBBS OB 15 JULY 1766 AE 33', the interior inscribed 'Vale Charissime' ('Goodbye, my dear'), mounted in gold, size M1/2