~ Understanding and Valuing Opals ~

By Stuart Bird (edited) - Webmaster for Internet Opals


When you are choosing your Opal it is VITAL that you know how the Opal will be worn, as some Opal will look brighter when viewed vertically whereas others will show more color when viewed horizontally.

This section sets out the factors used in determining value.

There is no governing body which has set the prices for Opal. Opal prices 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 from 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?

The type, color, 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.


Valuing Opal is very difficult and the following key factors are considered the most relevant in any appraisal.

Body Tone/Color - Black or dark Opal is considered more valuable than white or light Opal, technically Opals are rated according to their Body Tone "N" Value from 9 (black) down to 1 (light transparent)

Play of Color - The coverage of the play of colors is important, there should be no patches of inferior colorless Opal (potch) in a gem class or high grade Opal stone.

Colors in order of value in Australian Opal are:
1. Red
2. Violet
3. Orange
4. Yellow
5. Green
6. Blue

Dominant Fire Color: The clarity of the color is critical when assessing the value of Opal. Red Fire is the rarest color, followed by green/orange, green/blue and blue. Therefore red fire in an Opal is generally more valuable than a predominantly green Opal, which in turn is more valuable than a stone showing only blue color.

The brilliance and pattern of the colors present and the number of colors present. The intensity and clarity of the spectrum colors is very influential.

However, brilliance and clarity of an open proportioned 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 coloration or a brilliant, lustrous light Opal can cost more than a lackluster black opal.

Brilliance: The degree of brightness is of paramount importance as an Opal cannot be valuable without this attribute.

Brightness of Fire: (brilliance)
Shows a play of color only under direct sunlight, and even then, the fire is faint or almost non-existent.
Shows some color under low light, but is dull even under indirect sunlight or the grading lamp.
Shows fair color under low light and very nice fire under indirect sunlight or the grading lamp.
Very Bright
Shows good color under low light and sharp crisp color under indirect sunlight or the grading lamp.
Shows exceptionally bright crisp color under indirect sunlight or the grading lamp, and often shows even brighter in subdued light.

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 harlequin will only bring an average price.

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 expensive.

Solid Opals: Opal that has been mined and is presented either in its naturally occurring state or after being cut and polished.

It has not been chemically treated and has no other materials cemented to it.

Opal is made up of close packed aggregates of silica spheres, and with a water content between 3-10%.

In precious Opal the arrangement of spheres is in orderly layers, and light passing through the spheres is diffracted at the void and layer interface to produce the vivid play of color associated with Opal.

Larger silica spheres are associated with more sought after colors, such as red.


Color is almost everything in Opals. The more color the better, reds, pink, yellow and orange are harder to find, and therefore are more expensive, green, blue and violet are much more prevalent.

It is important to know the type of Opal, solid precious Opal is more valuable than doublet or triplet Opals.

Black Opal is more valuable than boulder Opal, which in turn tends to be more valuable than light Opal, the darker the body color, the more valuable the gem.

A stone with strong color and a full spectrum range is generally more valuable than one with a predominant red fire, which is more valuable than one with predominantly green color which in turn is more valuable than a stone showing only blue color.

Diffracted Color: 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 color has value in this order: red, orange, yellow, green, blue, indigo and violet. The red orange colors are the more valued. This rule is more particular to black Opal, "red on black" being the most valuable.

Base Color: Determined by looking through the top of the Opal beyond the play of color.

Body Color: With black Opal or black boulder Opal the degree of darkness in the body color must be taken into consideration. The blacker the body color the more valuable the gem.

Play of Color: Play-of-color of the Opal is the most difficult factor to judge for any Opal and does make a difference to the price for the end user.

Its brightness! * How bright is the overall play-of-color?

Its spectral range! * What range of colors is visible in the play-of-color ?

Its saturation! * How pure and vivid are the colors forming the play-of-color?

Its pattern! * What is the size, shape, regularity and rarity of the play-of-color?

Its consistency! * Is the play-of-color, pattern, brightness consistent or variable over the whole face of the opal?

Its directionality! * Is the play-of color visible from all directions as the opal is rotated?

Face-up Display:

This term is used to indicate whether or not an Opal, when viewed face on, presents its color directly to the viewer, the stone's value is less if its splendor is visible only from acute angles.

Many fine Opals, especially those with broad flashes of color, are at their best when viewed from a slight angle, these have special appeal when used as pendants or ring stones.

Consistency: Sameness in all the relevant characteristics of an Opal, including color, pattern, density of fire and color of the background.

Pattern Variety: Good patterns of the diffracted colors 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, almost all opal displays some form of pattern. You will never find two Opals that are exactly the same.

It's the amount of color and its intensity that makes it better than another.

In particular, many of the top quality pieces of black Opal from Lightning Ridge show their strength through a distinct recognizable pattern play of strong colors, some of the various patterns are listed below.

Harlequin Pattern: This is the most prized of all patterns and is very rare, the colors in this pattern are more or less arranged like checker board squares.

Floral Pattern: is possibly the most common of all nice patterns and its name is derived from its likeness to floral dress material, this pattern covers a broad range of design and color.

Pinfire Pattern: closely resembles a mass of pinheads in different colors.

Palette Pattern: is like an artist's palette.

Rolling Flash: Usually consists of one color that travels across part or all of the stone as it is moved.

Transparency: Natural precious Opal which is transparent to semi-transparent is known as Crystal Opal.

Crystal Opal, is a solid Opal which is transparent showing a play of color and no base color. This Opal will show little color when on a white background unless the colors are very strong and vibrant in it.

This Opal has a degree of transparency which allows the colors below the surface to be visible. Some believe the crystal varieties to be the most beautiful. Crystal Opals can be either light or black crystal, by definition, crystal Opal is any Opal, light, dark or black, that's clear enough to read through against a light surface but colors spring to life when viewed on any dark surface.

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

Crystal Opal can have either a black, dark or light body tone, the term "crystal" in this contest refers to appearance not a crystalline structure. Crystal Opals from Coober Pedy and Lighting Ridge are exceedingly beautiful and rare and command very high prices.

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

Shape and Polish: The usual shape for an Opal is a cabochon or domed oval, the length of which is about 40% greater than the width, and the height (dome) equal to about 60% of the width. In practice this is very difficult to find, because Opals have been fashioned irregularly by mother nature.

Perfectly shaped ovals generally command a premium price, because valuable Opal material is sacrificed when cutting them to this form. In most cases about 40-60% of the rough stone is ground away to produce the finished article.

Oval, pear and other regular shaped stones will bring a higher price than irregular shapes (freeshapes) because it is possible to obtain greater yields from freeshapes, and demand is higher for the regular shapes.

A cabochon enhances the appearance and signifies a thicker color bar or that it is skin-to-skin Opal. A domed stone is therefore more valuable than a flat or low domed stone. Black opals are not usually highly domed but are more likely to be flat on top or have a low dome.

The quality of the work performed by the opal cutter can significantly affect the value of the Opal. It should be polished so that no scratches or imperfections are visible to the eye.

Clarity: All Opals must be visually assessed for face-up clarity, any eye visible inclusion, such as patches of potch or lines of potch, (webbing) the presence of "sand spots" and/or crystals of gypsum near the surface or the Opal, or the presence of ironstone (in the face of boulder Opal), will effect the value of an opal. Importantly, the presence of crazing (surface-reaching cracks and fractures) in precious Opal renders it commercially valueless.

Appeal: Because Opal is so unusual the appeal of a particular Opal weighs more heavily than almost any other consideration. This is a double-edged sword, if it appeals to you as the buyer you will be willing to buy it but if it appeals to the seller you may have to pay extra to sever their emotional attachment.

Character: Some Opals are described as having character, which means their appeal is far greater than others of the same technical standard. Every person sees Opal in their own way, and an inexpensive stone can often have great personal appeal.

It's a fact that every Opal presents some different characteristic is very important, unlike other gemstones such as sapphires, rubies or emeralds, each Opal shows unique color combinations. It is rare to see two similar stones, and impossible to find two which are identical.

Opals with more attractive and appealing color combinations have higher values, the color patterns of many Opals appear as though they could have been painted on.

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 command a premium.

Imperfections: There are many types of imperfections which will affect the value, although sand, "cotton" and other impurities which are not clearly visible from the top of the stone have little impact.

Indeed, many collection quality opals will have sand in the back of the stones.

Cracks drastically reduce value.

A cracked or crazed Opal has very little commercial value unless the stone can be recut.

Cracks can be distinguished from inclusions and vertical color bars by examination with a strong light behind the gem. When the stone is tilted the examiner should see a glint of light reflecting from the crack, (except where a crack is silt filled) sometimes looks like a small brown fan inside, this is what is called a ginger whisker. On first impression vertical color bars and impurities such as copi may look like cracks but this simple test will clarify any doubt.

Another tip is to inspect the stone with a 10x loupe; if the mark breaks the polished surface, then it is a crack.

Weight:Opal is valued and sold by carat weight. 1 carat = 200 milligrams.

Photos of Opals:

Please keep in mind that taking photos of Opals is very difficult, much more so than of any other gem, often the Digital Camera picks up colors we do not see, but also seems to leave out some of what we DO see.

The Opal photos presented are a good likeness of the stones, but as with all Opal photos, they cannot show you all the true colors or Fire you would see in the real thing with some movement. So, if you think the opal looks good here, then it will always be better when seen with the naked eye in natural light.

The hardest and most difficult colors to photograph are the Blue/Green and the Green/Blue.

It should also be mentioned that Opals should always be viewed under close single incandescent light ( 12 to 15 inches away from the stone) or with the sun from over your shoulders, moving the stone in different directions for best play of color flashes.

~ Happy Shopping! ~


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