602
A Opal, Gem-set and Diamond 'Fish' Brooch, Stewart Young
Head set with a free-form opal slice, with a sapphire-set decorationBody set with circular-cut red spinelsHead and tail highlighted by tiny brilliant-cut diamonds18 karat pink gold
Full-Cataloguing
Precious opals show a play-of-colour when tiny spheres of amorphous silica diffract the passing light into its component colours. Among all the rainbow colours, red and orange are considered the most valuable, as seen on this brooch. Only when the spheres are arranged in a regular and repetitive pattern will the play-of-colour be evident. For the rarer red colour to appear, spheres has to be larger than the usual 150nm, but not more than 350nm. The more uniform the size of the spheres, the more intense, brilliant and defined the colour will be.