When buying an opal, there are a number of factors that must be considered in order to determine its value. These factors include the type, body tone, brightness, pattern, size and carat weight, clarity, and whether it is natural or hand-made. Having this know-how up your sleeve could mean that you get the best value for your price.
- Precious Opal – what makes this type of opal unique is its beautiful patterns and flashing colours when rotated. These are known as play of colours and occurs due to the size and arrangement of the hydrated silica spheres that makes up the opal. When light hits the opal and deflects off the spaces between the spheres inside the opal, the play of colours is produced. Blue and violet are more common while red is scarcer and therefore more valuable.
- Common Opal – this type of opal is usually milky in appearance and has no play of colours. This is because the hydrated silica spheres within the opal are not equally sized and are haphazardly arranged. The body colour can be white, grey or brown and in some instances even yellow, green or blue. These are found commonly around the world and are much less valuable than precious opals.
- Black Opals – these are generally the most expensive of all and are highly sought after. The play of colours in these opals is intensified by the dark body of the opals.
- Fire Opal – this is the term given for opals that have a yellow, orange or red body colour. They are often transparent or translucent. They may or may not contain the play of colours, although it is more common that they don’t. Fire opals are valued according to the colour with red being the most expensive, followed by orange and yellow.
- Boulder Opal – this form of opal is where a layer of precious opal forms on black ironstone rocks. Due to this, when the opal is cut, there will be a thin layer of the rock on the back of the opal. It may deceivingly look like black opal due to the rock’s dark appearance but is far less valuable.
- Crystal Opal – so named because of the transparent body that the Opal has.
- White Opal – The most common of the precious Opals. White Opal has a subdued play of colour because the white Opal background does not highlight the Opal colors.
Body Tone and Colour
This is another critical factor to bear in mind when selecting an opal and assessing its value. There is a range of body tones that opals may have, ranging from dark to light, with the darker tones generally considered to be more valuable. As mentioned before, this is because darker tones intensifies the play of colour. The Opal Association of Australia has developed the base body tone chart to help in determining the classification of Australian Opals.
This is the term given for the intensity of colours which is reflected when light penetrates the gemstone. There are three grades of brightness – Dull, Bright and Brilliant. Dull, also called Subdued, is the least bright and therefore the least valuable. Bright opals contain an average level of brightness and are more expensive than their Dull counterparts. Brilliant opals are the most expensive, are shinier and have the best play of colour.
Precious opals often display a variety of patterns. This is because of the diffraction of colours. Generally, larger patterns are equated with more value. When buying a precious opal, watch out for possible dead spots in the pattern. This is where there is no play of colour in sections of the pattern. These dead spots can reduce the value of the opal. Some popular patterns are mentioned below.
- Harlequin (or mosaic) is a pattern made of usually square colour patches, much like a mosaic. These are very scarce and if buying an opal with this pattern, it is best to buy it from a trusted seller. They can be very expensive.
- Chinese Writing patterns, as the name implies, resemble Chinese characters. It consists of short large strips of single colours that overlap. As with the Harlequin, this pattern is also highly sought after and valuable.
- Ribbon patterns are comprised of parallel strips of colour. If the bands contain different colours the value of the opal will increase.
- Picture stones are opals that have a pattern resembling a picture of some sort. This could be an object, a person or animal or even a landscape.
- Straw patterns are made of randomly arranged thin lines of colour. The more red the pattern contains, the higher the value is.
- Some other patterns that opals can contain are pinfire, flash, floral, moss and grass. While these are also beautiful patterns, they are considered less valuable.
Size and Carat Weight
While larger opals are generally considered more valuable, the size of an opal is not always commensurate with its value. Take for instance boulder opals, which can be large but may have less precious opal and more of the rock layer in its composition, thereby decreasing its value.
A number of factors can impact the clarity of an opal, such as natural flaws or inclusions. Flaws such as crazing (small cracks) on the surface the gemstone is a common blemish that can detract from its value. Inclusions can include sand or parts of the host rock that become a part of the opal. These can bring the value of an opal down.
- Doublet Opals – sometimes there can be precious opal that is too thin to be used in jewellery. This is then bonded onto a black backing to appear like a solid opal. To identify a doublet opal, look at the stone from the side. There will be a perfectly straight line where the two materials meet. However, once mounted in jewellery, it becomes nearly impossible to tell precious opal apart from doublet opal. As the value of doublet opals is less than solid black opals, ensure that you have bought this from a trusted jewellery seller.
- Triplet Opal – this is a hand-made stone where fine slices of precious opal are layered between a black backing and a layer of quartz or glass. It is not difficult to identify triplet opals by viewing it from the side. They are cheaper than doublet opals but over time, both these type of man-made opals become cloudy due to the deterioration of the glue used to hold the structure together.
- Synthetic Opals – these are created from scratch using the same chemical formula as their natural counterparts. While they can look exactly like natural opals, the differences will be in terms of pattern and density. The patterns often have an impeccable arrangement and resemble snake-skin, while the density is lower than natural opals. Synthetic opals are cheaper than natural opals.
In the nutshell, all the mentioned factors should be taken into account when buying an opal. However, it is very important to note that valuing an opal is an extremely difficult task and requires a lot of experience. Therefore, the best way to avoid over-paying is to buy opals from reputable dealers who have gemmological qualifications and will provide you a certificate of genuineness.
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