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brilliant crystal opals
semiblack to black
high transparency
low quality black opal
high quality black opal
PRESENTATION OF OPAL

Valuing Opals

The following paragraphs are also reproduced with permission from Andrew Cody's book:

"This section sets out the factors used in determining value. There is no governing body which has set the price for opal; they are a result of what the international market is prepared to pay in order to obtain the gem. As with any other commodity, opal is subject to the laws of supply and demand. The supply of opal is never guaranteed - the luck of the miner, variable costs, new discoveries, floods and weather conditions - all affect the supply of the stone.

Demand relates to the enthusiasm of the customer for opal, and may be influenced by fashion and market trends. For example, the unprecedented demand over the last few years for fine quality opal, particularly by Japanese customers, has caused prices to soar."

The attractiveness and appeal of a particular opal are the factors which are important at the final point of sale. What makes up this attractiveness and appeal?

These are described in the following sections:

Type
Brilliance
Pattern
Body Colour
Transparency
Diffracted Colour
Thickness of Colour Bar
Shape
Size

Type

It is important to know the type of opal. For instance, a black boulder opal could in all respects be the same as a black opal, except that the black opal will be approximately three times as valuable.

Brilliance

The degree of brightness is of paramount importance. An opal cannot be valuable without this attribute. A gem that glows but is average in all other respects will still command a high price whereas a dull stone with a very good pattern such as a harlequin will only bring an average price. The photographs used in the grading scales of this book depict the brilliance and intensity gradient.

Pattern

Good patterns of the diffracted colours when combined with brilliance have an enormous impact on the value. Pinfire and small type patterns are less desirable than broad patterns or large flashes. Distinct patterns such as rolling flash, straw pattern, Chinese writing, ribbon and harlequin are very rare and considered collectors' items.

Body Colour

With black opal or black boulder opal the degree of darkness in the body colour must be taken into consideration. The blacker the body colour the more valuable the gem.

Transparency

Light opal is more desirable when it has a degree of transparency and if lively brilliant colours are present in crystal opals, they are most highly prized. However, transparency in black opal will generally reduce its value.

Diffracted Colour

Great care needs to be taken when applying this factor, remembering that brilliance overrides all other factors. A blue/green brilliant stone will usually be more valuable than a dull red stone. The dominant colour has value in this order: red, orange, yellow green, blue, indigo and violet. The red orange colours are the more valued. This rule is more particular to black opal, 'red on black' being the most valuable.

Thickness of Colour Bar

Black opals and black boulder opals with a very thin colour bar are frequently worth many thousands of dollars a carat, although they would be worth more if they had exactly the same appearance with a thicker colour bar. Thickness of bar would also enable a cabochon to be cut from the rough, thereby increasing value.

Shape

Oval, pear and other regular shaped stones will bring a higher price than irregular shapes (freeshapes). Although it is possible to obtain greater yields from freeshapes, the demand is higher for the regular shapes. A cabochon enhances the appearance and signifies a thicker colour bar. A domed stone is therefore more valuable than a flat stone. Black opals do not usually have a cabochon.

Size

Smaller sizes under a carat are worth less per carat than larger stones. This is particularly true with black opal, although less important if the stones are calibrated. Larger stones are harder to obtain and can sometimes command a premium.'