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With the demand for vibrant gemstone growing almost daily, vendors must find new ways to push lower-quality stones into the upper echelon of the market; this has led to the rise in ‘gemstone treatments’. These are procedures that, as the name might suggest, are meant to enhance a gemstone's appearance or stability. Although treated opals can look quite beautiful, ethical problems arise when a seller does not disclose the treatments used on their gemstone. 

In the past years, as online sales have risen in popularity, there has been a steep increase in the amount of treated Welo opal that is being marketed as natural black opal. In addition, there are various listings for treated Ethiopian opals that are being wrongly listed, with a prevailing issue of such products being sold in Australia retail shops, and (unfortunately) also in opal fields.

Why are Opals Treated

There are many different reasons why an opal would be ‘treated’. In recent years, various Queensland boulder opal specimens have been treated by the deposition of a layer of Aluminium oxide (Al2O3). This is done specifically to overcome the inherent softness of the opal. 

Some opals are heat treated. An opal's colour will be brighter when the surface is sprayed with a liquid such as water. Wetting the surface of a rock will only change the colour for as long as it takes for the liquid to dry; a more permanent solution is for the opal to be treated using heat and oils. Another permanent solution is to soak and simmer the stone in a sugar water solution for several hours, so that the acid in the liquid solution can carbonise, but this is usually only done to opal that as formed in sandstone, as the background colour of sandstone is quite light meaning the opals colour does not appear as vibrant. The end result of this procedure is that the colours of the opal will be much more vibrant, giving the appearance of a black opal. 

The action of treating an opal is not inherently bad, it is only when these opals are then marketed as otherwise, and people are deceived, that this becomes a problem. 

Opal Marketing - A Clever Trick 

‘Black Opal’ gets its title from the dark colours in its stone. Although natural untreated opal is often found in Australia, countries such as Ethiopia, USA, the Czech Republic, Hungary, Mexico and most recently Indonesia, can have genuine opal found in their soil. The issue is not the origin of the stone, but rather, the treated opals are being sold as natural black opals. Sellers who omit the truth and push treated opal as ‘the real deal’ are taking advantage of others, preying on the current lack of information within consumer circles. 

Treated opal has its place on the current market, however, currently it is being sold through manipulation of words, peddling the stones through false means. 

The term ‘Natural Black Opal’ is being used to describe the gemstones in an online purchase. Although, technically, this description is true - the opal is found from the ground, therefore is natural, and the gemstone is black in its colour - the words used are for the purpose of deception. The current market is so flooded with ‘so called black opal’, that in previous years, the term not only refers to genuine black opal, but is grouped in with dyed, smoked, or sugar-acid treated Ethiopian opal. 

This concerning trend sheds a light on the inherent nature of the opal industry, but there is still hope. Although the methods of determining whether a gemstone is ‘natural’ or not can be questionable at times, there is still an effort from trustworthy retailers to ensure that their consumer base is not being lied to through omission. 

Customers are being deceived, and that is a problem. Buying natural untreated black opal from the heart of Australia is always going to be what an individual wants, and when a stone is significantly altered to produce a black body colour, then sold at a price over 500% its actual value, then it is simple to say that the trust between jewellers and their clientele can rapidly deteriorate.  

Image depicting an opal before and after being treated. 

How to Tell if an Opal is Treated 

A respected laboratory or jeweller will probably not be available nearby when you purchase opals online or at a field/marketplace. There are ways to tell if a stone has been altered, most of which require simple household objects. 

Many treated opals will display telltale signs of tampering, the most noticeable being dye or smoke marks on the back of the stone, indicating that the black on the back of the opal is not natural and has, in fact, been tampered with.   

Other treated opals will have signs of tampering, but they will be more subtle. For instance, treated black opal from Ethiopia - when a strong yellow light is shone closely underneath the stone - the opal will have a deep cherry red transparency (whereas untreated black opal is generally very dark brown or grey); If the background colour is hard to discern, try focusing on an area with a minimal amount of colour. This effect can be achieved with something as simple as a phone camera or flashlight, which both can be used to get a closer and more intricate look of the physical appearance of the stone, possibly aiding you in detecting treatments. An important thing to remember is that white light (although it may appear yellow to the human eye) includes the entire spectrum of colours that are visible to humans, and therefore is a crucial tool in seeing the true colours of any stone, treated or otherwise.

Black opal is one of the rarest gemstones on earth. If you happen to notice that the stone is highly domed, or stone colour can be seen through the opal, being visible on the front, back, and edges of the stone, then you should proceed with caution, as this combination of a high done and full colour is extremely rare in natural untreated black opal. Overall, proceed with caution if: 

• Upon closer inspection, the body colour of the opal is jet black
• The transparency of the stone (when seen under yellow light) is a deep cherry red colour 
• While the stone is immersed in water (and a strong light source is present) distinct dye or smoke marks become apparent

Synthetic Opal

Synthetic opals are a man-made stone, created with the same internal composition, structure, and properties and natural opal. However, with the creation of these ‘lab-cheated’ gemstones, comes the rising need for cheap and quick jewellery; man-made synthetic opal can fulfill this need. This, overall, has led to not a misinformed price and quality that has now become commonplace for cheaper alternatives, but has also aided in the perpetuation of distrust between jewellers, and those wishing to buy genuine opal. 

Originally created in Switzerland, Gilson opal is now primarily synthesised in Japan. This type of Opal has been around since 1974. It is created using Silica so it is a true synthetic version of natural Opal. ‘Gilson opal’ as a term is often used in reference to imitation opals, which are gems that are not only man-made, but contain minerals and materials that cannot be found in natural opals. 

Ethiopian Opal

Currently we do not stock or sell Ethiopian opal. The Ethiopian Opal comes out of the ground looking like a brown beer bottle and requires substantial treatment to get it to show colour. The chemical treatment is effective but is not permanent. We have been contacted by numerous customers who have suffered the shock of this treatment being reversed. This is a problem that the world bank suggests goes right back to a failure in policies set by the Ethiopian government. The customer is often not told about this....and this is the problem.

This can be a tricky thing to navigate, as technically the opal is ‘genuine’, there are just negative side effects of prolonged usage that may not be disclosed upfront. 

Overall, it is important that you stay aware and inform yourself of what to look for when purchasing opal, so that the various tricks intended to ‘dupe’ you can be avoided, and you can be happy and secure in your purchase.