There are many factors affecting the value of Opal. The type of Opal, body tone, brilliance, pattern and colour all play significant roles in determining the value.
Type of Opal
First of all, it is important to identify the type of the Opal. The Black Opal is considered the most valuable Opal; it is the rarest Opal. People may be more familiar with light opal, which is the most common Opal.
The degree of darkness in the body tone of a Black or Boulder Opal is taken into consideration when valuing the Opal. Body tone refers to the background of the opal, which can range from black through to light. A black body tone is rarer and more valuable than a grey, light or white body tone because a stone with a deeper body tone tends to have more vibrant colours.
The degree of brightness is of utmost importance. Brilliance refers to the brightness and clarity of the colours displayed by the Opal jewellery. The bright stone that glows is considered rarer than a dull stone. A cloudy or milky background colour lowers the value and makes the Opal less attractive.
Interesting patterns of the diffracted colours are rare and, when combined with brilliance, have an enormous impact on the value. You can find patterns like, pinfire, rolling flash, broad flash, straw pattern, floral pattern, picture stone, Chinese writing, ribbon pattern and harlequin. The harlequin pattern is the rarest and very rarely found.
Red opal is generally more valuable than a mainly green and blue stone. However, a bright green and blue stone will usually be of more value than a dull red stone. There are numerous other colour combinations from which to choose; blues, greens, oranges and purples. Deep red and orange colours on Black Opal in a dark body tone is the most valuable. It is the variety of colour and pattern that makes the Opal so unique and valuable.