In the 19th century, a rumour spread by Walter Scott’s novel Anne of Geierstein, crediting it as an unlucky, proved prejudicial to the popularity of the opal. But eminent figures such as Queen Victoria, sovereign of Australia which is the home of the incomparable Harlequin and Black opals, had access to the most prestigious gems. Not only did she adorn her regal jewellery with them, but also that of her daughters and granddaughters. The opals of the Hofburg Treasury now on show in Vienna are famous, and include the major collection of Princess Stephanie of Hungary.
Patrick Voillot, the grand gemstone specialist and the brains behind the Gemmology Museum that has just opened at Chatenay Malabry, Paris, explains that although opals had long been thought to bring bad luck, there is no truth in this poor reputation which is due solely to its fragile nature. Because of the sedimentary process resulting from a concentration of silica gel in former evaporated sea waters, opal contains a quantity of water representing between 3 and 10% of its total weight. This is why it must be protected from heat or from intense light, which may cause this water to evaporate and thus cause fractures. Ultrasound waves, acids or powerful solvents must also be avoided. While many opals originate from Australia, Van Cleef & Arpels uses exclusively opals from Ethiopia, where the mines were only recently discovered. This year, Cartier has introduced some splendid creations in which opals are highlighted in new and unexpected ways.
The play of colours characteristic of opals is caused by the diffraction of light passing through the transparent spherical particles of crystobalite, a form of silica, and the spaces in between these microscopic particles with a diameter equivalent to 1/1,0000th of a millimetre. Opals are classified into three types serving as a background for the play on colours. These three types: are black opal, white opal and transparent opal. Several sub-categories result from the quality and the spread of the colourful patches. The most famous are Harlequin, flash, flame and pinfire. Some types of opal do not feature this play on colours : these include most of the orange stones called fire opals, a green variety known as prase opal and a blue variety found in Peru. This mysterious fine stone with its myriad shimmering reflections still has plenty of surprises in store for us and has doubtless not said its last word.