Many attempts have been made to establish a definitive guide for valuing the price of precious opal, however, they've mainly been unsuccessful because, unlike other gemstones, opals tend to be unique, with infinite variation in pattern and brightness.
Things commonly looked at when valuing an opal are:
- Background colour - black opal and dark opal (so an opal with a dark background) is generally more valuable than clear and amber opal (crystal or jelly opal) which, in turn, is normally more valuable than a white or milky opal.
- Colour play - Australian opals showing red fire are generally more valuable than stones showing green fire, which, in turn, are generally more valuable than those showing blues and purples.
- Number of colours - Australian opals showing more than one colour are generally more valuable than those only showing one (with the exception of predominant reds). Opals that show more than three colours are referred to as 'multi-coloured opals'.
- Colour pattern - harlequin or flagstone opal, where the colour occurs in patches, is generally more valuable than a pinfire opal where the colour is in small, pin sized, specks. That said, there are many other colour pattern presentations, such as ribbon, honeycomb, broad flash, rolling fire and skin-to-skin, and all of these will affect the price in conjunction with the above factors.
- Mine - the actual mine the opal has been taken from can also affect the price, with opal from depleted mines being increasingly sought after.
- Cut - there is a marked difference between the value of an uncut opal and that of a cut and polished stone, not least because of the difficulties involved in cutting and polishing such a 'soft stone'.
Opals may be cut and polished in a number of ways and the way an opal is cut can also dramatically effect its price - and a buyer should be made aware of exactly what kind of opal they are buying:
Generally the most expensive kind of opal is a solid opal (brightness and pattern factors being taken into account). Solid opals are always the most desirable kind of opal, especially if you are looking at carat weights!.
A doublet cut opal is where a thin veneer of opal has been applied to a dark or black backing (most often), this may or may not be a 'potch opal' backing.. This can enhance the initial colour play found in the thin sliver of opal and mimic a very high value solid black opal.
A triplet cut opal is where a thin slice of quartz is used to cap the top of the opal veneer to protect it from abrasion, whilst the back of the opal still has a backing applied (so, basically, there are three parts to the original opal -- a quartz layer, an opal layer, and a backing layer). This is a very cheap method of production and triplet stones are generally cheaper than doublets.
Doublet and triplet cut opals should always be kept away from water, as the water can seep into the stone through the sides and crack the opal sliver. In comparison, water and solid Australian opals usually pose no problem and, in fact, it is often recommended to wipe your solid opals down with a wet cloth to help protect them from drying out.
We would always suggest that, when buying an opal, personal preference is also taken into account... For instance, they may not be the most valuable opals, but we go absolutely nuts for bright purple crystal opals, especially if the fire is in a broad wash and in conjunction with yellows. We also love a good confetti or pinfire opal.