Black opal and diamond ring, 1920s. Black opals are a particular variety of iridescent opal famed for their dark body colour, against which the play of colour seems even brighter. Black opals are primarily sourced from an areas of Australia known as ‘Lightning Ridge’, and since their discovery in the 19^th century they have been the most highly valued variety of opal. The play of colour in opal is down to the fineness of its internal structure, and consequently no two are the same, and some colours are rarer than others. This opal is particularly unusual for its large, rolling flashes of red, which is the rarest colour in opal, and also for the patchwork pattern in which these colours appear, reminiscent of the most highly-valued ‘Harlequin’ opals. Showcasing this extraordinary central stone is a beautiful early 20^th century foliate mount set with single-cut and baguette diamonds – the delicate sparkle of the diamonds providing the perfect complement to the opal’s bold flashes of colour.