The brightness of the colour is most critical when assessing the value of opal. Red is the most sought after colour, followed by orange, gold, green, blue & violet. Therefore red opal is generally more valuable than a predominantly green opal, which in turn is more valuable than a stone showing only blue colour. However, brilliance, darkness & pattern are the main decision makers - a brilliant blue/green can cost more than a dull red; bright twinkling stars of a 'pinfire' pattern can cost more than a cloudy open pattern of similar colouration; or a brilliant, lustrous light opal can cost more than a lacklustre black opal.
The type, colour, size and soundness of precious opal are factors that determine the price paid for the gemstone. The price is based on the quality of the opal and expressed per carat. Furthermore, there is a marked difference between the value of uncut opal compared with the value of cut and polished opal.
Almost all opal displays some form of pattern. You will never find two opals that are the same. In particular, many of the top quality pieces of black boulder opal show their strength through a distinct recognizable pattern play of strong colours. Some of the various patterns are listed below.
Harlequin is extremely rare and the most prized pattern, this consists of the colour pattern resembling a near perfect checker board.
Floral is possibly the most common of all patterns as it covers a broad range of shapes & designs, somewhat like the floral pattern on a ladies dress.
Pinfire is the arrangement of colour with the appearance of stars or small dots in the stone.
Brush Strokes some what resembles a painters pallet with the large odd shaped blotches of different colours.
Rolling Flash is more common where one predominate colour travels across the stone as it is moved.
BACKGROUND OPAL COLOUR OR BODYTONE (BODYTONE CHART)It is important to know the type of opal. Solid precious opal is much more valuable than doublet or triplet opals. Black Opal is more valuable than semi-black, which in turn is more valuable than light opal. The darker the body colour, the more valuable the gem.
The body tone of an opal is different to the play-of-colour displayed in precious opal. Body tone refers to the relative darkness or lightness of the opal when ignoring the play-of-colour.
Black Opal - is the family of opal which shows a play-of-colour within or on a black body tone N1, N2, N3 and N4 are viewed as black opal.
Dark Opal - is the family of opal which shows a play-of-colour within or on a dark body tone, N5, N6 are viewed as dark opal or semi-black opal.
Light Opal - is the family of opal which shows a play-of-colour within or on a light body tone N7 and N8 are viewed as light opal. The N9 category is viewed as white opal.
Example Of Very Bright Colour
Solid opals are a natural stone that is mined out of the ground and simply cut and polished with no additives or glued backs or caps on them and these are obviously the most valuable form of opal, fetching anywhere up to $10000 per carat.
Opal Triplets are a very thin slice of precious or crystal opal glued to a black base of glass, potch or semi precious stone such as tourmaline and covered with a clear natural crystal cap, as the name implies a triplet contains 3 layers.
Opal Doublets are a thin section of either precious or crystal opal, glued to a glass, potch or tourmaline backing, but with no crystal cap to cover the opal, doublets only consisting of the two layers.
Synthetic opal is produced in the laboratory and has a similar structure to that of precious opal. The following observations can be made to differentiate between natural and synthetic opal. Synthetic stones show brighter colours, and larger colour patches than in natural opal. In synthetic opal, colour grain boundaries are highly regular. Synthetic opal has a distinctive snakeskin pattern. Synthetic material shows a more ordered array of colours because the intricate pattern of natural opal cannot be duplicated.
Doublet, Triplet and synthetic opal can have the appearance of a high quality opal to the untrained eye but are of a very low value and you should always understand exactly what you are purchasing, these may be a good option for a bright piece of opal jewellery on a small budget but will not be and investment and are of no comparison to the real thing.
A solid Australian opal can be a great long term investment and will never go down in value or deteriorate, the many myths about opals and their issues surrounding water and oil are all related to the layered opals and not true in any way about solid opals.