Additional Learning
Below are the different treatments, enhancements and other such information pertaining to opals.
Treatments and Enhancements
Treatments and enhancements are utilized in the opal industry for a variety of purposes. This can include stabilizing a stone, altering the body tone of the stone, and other such modifications. Due to the nature of these treatments and ehancements it is important to understand what they do, why they are used, and how to identify them when possible.
Sugar-Acid/Sugar-Bake Treatment
One of the more traditional opal treatments is known as the sugar-acid process. This technique has been used especially on light-coloured opals from places like Andamooka in South Australia. In this method, the opal is first soaked in a sugar solution, allowing sugar molecules to seep into the stone’s porous structure. Then the opal is placed in sulfuric acid or slowly baked in a tin of dry sand, which carbonizes the sugar inside, darkening the opal’s body colour.
The darker background makes the flashes of colour stand out more vividly, giving the stone an appearance similar to natural black opal. While this can produce attractive results, it’s considered an artificial enhancement and treated stones typically hold less value than untreated black opals. Buyers should always be informed when this treatment has been applied.
Smoke Treatment
Smoke treatment is commonly associated with Ethiopian opals, many of which naturally have a lighter or milky body colour. The goal of this process is to darken the background of the opal, making its play-of-colour appear more dramatic. To carry it out, the opal is wrapped in paper and gently heated so that smoke infiltrates the stone, leaving fine carbon particles embedded within.
This treatment can create visually striking gems, but it’s important to know that smoke-treated opals can sometimes fade if exposed to heat or certain chemicals over time. Ethical sellers should disclose this treatment so buyers understand how to care for their stones and what to expect from them in the future.
Dyes
Some opals, particularly lower-grade or pale stones, may be dyed to produce more vibrant colours. This involves introducing artificial pigments to change the opal’s body colour, resulting in shades such as black, blue, green, or other striking hues.
Although dyed opals can look beautiful, the treatment is purely cosmetic and the colour may fade or bleed over time, especially if the stone comes into contact with water or chemicals. Dyed opals usually have a lower market value than naturally colourful stones, and it’s essential for sellers to be transparent when dyeing has been used.
Oils and Other
Certain opals, especially hydrophane types from Ethiopia, can be porous and prone to cracking or losing moisture. To help stabilize these stones, some are treated with colourless substances like oil, wax, or resin. This process can fill small fractures, improve clarity, and enhance the stone’s surface polish.
While this treatment can make opals more suitable for use in jewellery, it’s still considered an enhancement and should be disclosed. Over time, the appearance of treated opals may change slightly, particularly if the stone is exposed to heat or cleaning chemicals.
Doublets and Triplets
A significant portion of the opal jewellery market involves doublets and triplets. These are not treatments in the sense of changing the opal’s chemistry, but rather ways of assembling thin layers of opal into more durable or visually impactful stones.
A doublet consists of a thin slice of opal bonded to a dark backing, like ironstone or black glass, which makes the colours stand out more vividly. A triplet goes a step further by adding a clear protective cap—often quartz, glass or lab grown white sapphire—on top of the opal layer. These constructions allow thin opal seams to be used in jewelry that would otherwise be too fragile or small for setting on their own.
Although doublets and triplets can look beautiful, they are not solid opals and generally hold less value. They also require more cautious handling, as water can sometimes seep between the layers and damage the adhesive. As with other treatments, these assembled stones should always be clearly identified when sold.
Stabilizing
Stabilization is a treatment used to improve the durability and appearance of certain types of opal, especially those that are porous, brittle, or prone to cracking. Some opals, such as Ethiopian hydrophane opal or matrix opals from Honduras or Andamooka, have tiny pores or fractures that can make them fragile or vulnerable to absorbing water or other substances.
In stabilization, the opal is soaked or vacuum-infiltrated with a clear substance like resin, polymer, or plastic. This material fills the pores or fractures, helping to strengthen the stone and prevent it from cracking or losing water. In some cases, stabilization can also slightly improve the opal’s clarity or deepen its colour, although the goal is primarily to make the stone more durable and suitable for use in jewellery.
While stabilization can be a very effective way to preserve opals that might otherwise be too delicate for everyday wear, it is considered a treatment and should always be disclosed to buyers. Stabilized opals generally have a lower market value than untreated stones, because they are no longer entirely natural in structure. However, they can still be beautiful and long-lasting if properly cared for.
Identifying Natural vs Synthetic Opal
Synthetic opals have been part of the gem world for decades, first appearing in the 1970s when companies like Gilson figured out how to grow opal in a lab. These stones are made from the same material as natural opal—tiny silica spheres—but they’re formed under controlled conditions rather than over millions of years in the ground. Because of this, synthetic opals share the same colourful flashes and overall look, but they’re generally less valuable since they’re not rare or naturally occurring.
One of the easiest ways to tell the difference is by looking at how the colours are arranged. Natural opals usually have patches of colour that vary in shape and size, giving them a random, almost painterly look. Synthetic opals, on the other hand, often show a repeated, organized pattern that can look a bit too regular. People sometimes call it a “lizard-skin” or “snake-skin” pattern because of its scale-like appearance.
Another clue comes from looking at the opal from the side. Synthetic opals often show a sort of layered or column-like structure because of how they’re grown in the lab. Natural opals don’t have this kind of organized layering. Plus, the colours in synthetic opals can sometimes appear almost neon or overly bright, lacking the subtle shifts and variety found in natural stones.
Checking for inclusions can also help. Natural opals often have tiny bits of sand, rock matrix, or small internal cracks—reminders of their formation deep underground. Synthetic opals usually look much cleaner and more uniform, without those natural imperfections. Sometimes the body colour in a synthetic opal can seem almost too pure or evenly distributed, especially in types like black opal.
Although visual clues are helpful, gemologists often rely on tools like microscopes, spectroscopes, and other laboratory methods to confirm whether an opal is natural or synthetic. Understanding how to distinguish between them is valuable knowledge for anyone interested in gemology, mineral collecting, or even the science of how minerals grow. Synthetic opals are fascinating in their own right, demonstrating the remarkable ways human technology can replicate nature, and studying them deepens our appreciation for both natural gems and the skill involved in creating their lab-grown counterparts.