When light strikes an Opal and creates a brilliant colour display, the traditional mystic explanation has been that the colours signify a favourable response heralding success and good fortune. When the light creates a dull reflection of colour from the Opal, interpreters have usually taken that for an unfavourable response – failure and disappointment will soon follow!

The name Opal is derived from an Indian word for “stone”. There are three groups of Opals: Common, Precious and Fire. Common or Potch Opal is opaque with no play of colour. Precious Opal, which is the one that most people think of as Opal and the type most used in jewellery, is prized for its opalescence. Fire Opal, named after its bright orange colour, is a transparent orange variety of Opal with no opalescence. As it is transparent, it usually cut in a faceted style. Whereas precious Opal, which is at best translucent, is cut as a shallow cabochon to display its opalescence.

The unique characteristic of Precious Opal is the play of colour caused by the Opal’s structure, which can be revealed under a magnification of 17,500.   It is made up of row upon row of tiny spheres of silica in a siliceous “Jelly”. These tiny spheres diffract light into the different colours of the rainbow and their exact size affects the colours produced. The slightly larger spheres produce a greater range of colours favouring reds and oranges, whereas the smaller spheres will tend to favour greens and blues.

There are two types of Precious Opal: White Opal is the more common form and as its name suggests the “body” colour is white or milky. The rarer Black Opal has a dark greyish body colour – very rarely is it actually black

The greater the play of colours the more desirable the stone. The play of colour of all Opals always appears more dramatic when placed on a black background. This is part of the reason why Black Opal is considered a better looking stone than White Opal. This fact is used to great effect in the production of Opal Doublets, and Triplets. With the Doublet a thin slice of Opal is glued onto a piece of onyx and this imitates a better quality Black Opal. The Triplet is produced in a similar way with the addition of a protective layer of colourless quartz on top. If these stones are then mounted in a closed-back setting in a piece of jewellery they provide a convincing imitation of Black Opal. A trained eye using a jewellers x10 lens will easily spot the masquerade.

Opal is also unique in being the only non-organic gemstone having water in its chemical composition. It should be no surprise therefore that it is the most delicate gemstone – not only is it soft, but as it contains 5 – 10% water, it may dry out and crack. Conversely, if the Opal is soaked in water it may expand.  Soaking an Opal in pure baby oil can stabilise the stone. The Opal is porous and soaks up the oil and can not absorb or lose any water. If setting Opal in a rub-over setting it will be afforded some protection from knocks by the gold that covers all its edges. Unlike most other gemstones Opal is not crystalline; it forms by the slow solidification of a jelly within cavities in rocks. Since the end of the 19^th century Australia has been the main producer of Opal (Black Opal is only found in Australia). Before then the finest quality Opal came from Czechoslovakia.

In common with all other gemstones there are many myths surrounding Opals. At one time they were considered to be a favourable stone for “Affairs of the Heart”.   Should one lover be unfaithful, the Opal’s good influence would be reversed upon the unfaithful lover! This was interpreted as Opals bringing bad luck in love and Opals were deemed to be an unlucky stone to have in your engagement ring.  A belief that is still widely held today.