A Gem Dealer’s Guide to Opals: History, Treatments & Market Insights

The Fascinating World of Opals
Opals have captivated jewelers and collectors for centuries, not just for their hypnotic play-of-color but also for the myths and stories woven around them. The Romans saw opals as symbols of purity and fortune, while in the Middle Ages, they were believed to hold the powers of all gemstones combined. As someone who works with opals daily, I can say that no two stones are alike, making them one of the most exciting gems to trade.

Types of Opals and Their Origins
In the gem trade, opals are classified into several main types: black opals, white opals, crystal opals, and fire opals. The most coveted are Australian black opals from Lightning Ridge, known for their deep body tone that amplifies color play. Ethiopian opals, with their jelly-like transparency and fiery flashes, have taken the market by storm in the past decade. Mexican fire opals, often orange-red and sometimes faceted, are a different beast altogether, prized for their clarity rather than their play-of-color. Brazil, Indonesia, and even the U.S. have opal deposits, but they are less commercially dominant.

How Opals Are Enhanced & What to Watch For
Not all opals on the market are untreated. Smoked, sugar-acid treated, and composite (doublet/triplet) opals can offer beauty at a fraction of the price of natural black opals. Smoking and acid treatment darken the background of white opals, intensifying their color contrast. Doublets and triplets, on the other hand, layer thin opal slivers onto darker backing material. While these treatments can make an opal visually stunning, they should always be disclosed by the seller.

Luxury Brands Embracing Opals
High jewelry houses have recognized opals as statement gems. Cartier, Tiffany & Co., Van Cleef & Arpels, and Dior frequently feature them in their collections, often playing with their dreamlike patterns in avant-garde designs. One of my favorite recent collections was Dior’s opal-studded ‘Archi Dior’ line, where opals were paired with diamonds to create an almost ethereal glow.

Smoked Opal: A Black Opal with a Secret

Everyone dreams of owning a true Australian black opal, but the price can be staggering. Enter smoked opals—stones that mimic black opals through treatment yet still hold value in their own right.

What is a Smoked Opal?
A smoked opal is a natural opal that has been darkened artificially by exposing it to smoke or burning organic material. This allows microscopic carbon particles to enter the stone’s structure, creating the illusion of a deep, black body tone. The result? A much stronger contrast in play-of-color, making the opal resemble its pricier Australian counterpart.

Another Method: Sugar-Acid Treatment
A different technique involves soaking the opal in a sugar solution before exposing it to sulfuric acid. This causes a chemical reaction that forms dark carbon deposits inside the stone, once again deepening its color background.

Why Do Treated Black Opals Still Hold Value?
Not every opal can be treated successfully. The base stone must have strong play-of-color to begin with—otherwise, no amount of darkening will make it visually appealing. Well-treated opals can be a great entry point for collectors who want the black opal look without the five-figure price tag.

How to Spot the Difference?
Genuine black opals are naturally dark and mined exclusively in Lightning Ridge, Australia.
Smoked and acid-treated opals appear darker only on the surface, which can be detected under a microscope.

While nothing compares to the beauty of a natural black opal, smoked and treated opals offer an accessible and visually stunning alternative for collectors and jewelry lovers alike. The key is to be informed and buy from reputable sources to ensure you know exactly what you are getting.

Opals and Water: Debunking the Myths
A common belief is that opals are extremely fragile and should never come into contact with water. This is a misconception.

Can Opals Get Wet?
Yes, opals can be safely exposed to water. Natural opals contain water (typically 3-10%), but brief exposure will not damage them. Washing your hands or getting caught in the rain will not ruin an opal.

What Should Opals Avoid?
While water itself is not harmful, extreme conditions can be. Opals are sensitive to sudden temperature changes, which can cause cracking. Harsh chemicals, such as acids, detergents, or perfumes, can affect the stone’s surface or alter its play-of-color.

How to Dry an Opal Safely
If an opal gets wet, simply pat it dry with a soft cloth and allow it to air dry naturally. There is no need for excessive heat or drying techniques.

Faceted Opals: Rarity or Mistake?
Most opals are cut into cabochons to highlight their play-of-color. However, faceted opals do exist, particularly with fire opals and some Ethiopian opals.

Why Are Opals Rarely Faceted?
Opals are relatively soft (5.5-6.5 on the Mohs scale), making them prone to chipping. Faceting increases the risk of damage and can disrupt the natural light play that makes opals so unique.

When Does Faceting Work?
Transparent opals, like fire opals, can benefit from faceting, as it enhances their brilliance. Some Ethiopian opals, due to their clarity, are also faceted for a more gemstone-like appearance. 

While traditional cabochon cuts remain the industry standard for opals, faceted opals can be a unique and eye-catching choice when handled with care.

Opal – Not a Mineral? Let’s Find Out! 

Most gemstones we know are minerals, meaning they have a defined crystalline structure. But opal is the exception. It doesn’t have a strict atomic order—instead, it consists of amorphous silica. This means its structure is neither fully crystalline nor completely chaotic—something in between. And that’s exactly what makes opal so special!

How is Opal Different from Minerals?

1️⃣ Minerals have a strict atomic arrangement following crystallographic laws. Opal, however, has an amorphous structure with no fixed atomic pattern.

2️⃣ Instead of a crystal lattice, precious opals contain silica spheres—microscopic, round particles stacked in layers.

3️⃣ Because of this structure, opal doesn’t have a fixed hardness—it ranges from 5.5 to 6.5 on the Mohs scale.

4️⃣ Opals contain water—up to 20%! 💧 This makes them sensitive to drying out and humidity changes.

What Does This Have to Do With Opalescence?

Opals glow like liquid light because of their unique structure. The tiny silica spheres are arranged in a way that refracts and scatters light, creating interference and diffraction—the mesmerizing play-of-color effect known as opalescence.

• If the structure is random (as in common opals), there’s no color play.

• If the spheres are arranged in neat layers (as in precious opals), the result is an incredible iridescent display.

Does This Mean Opal Isn’t a Gemstone?

Of course not! Even though opal isn’t a mineral in the traditional sense, it is still considered a precious gemstone and is highly valued in gemology. In fact, its unique structure is what makes it so extraordinary.

In the world of gemstones, opal stands in a category of its own, proving that nature can create something truly one-of-a-kind. 

Opals from Czechia, Slovakia, and Moldova – Hidden Gemological Treasures

When people talk about opals, most immediately think of Australia, Ethiopia, or Mexico. However, there are other, lesser-known but equally interesting deposits in Czechia, Slovakia, and Moldova. These opals are almost never seen on the market, and there are several reasons for that.

Why are they so little known:

• Limited mining volumes – these deposits have never been major suppliers, so their stones rarely reach the global market.

• Quality characteristics – Czech and Slovak opals often have less intense opalescence compared to Australian ones, while Moldovan opals are usually semi-transparent or matte.

• Historical factors – the deposits were never developed on an industrial scale, and local stones rarely made their way into jewelry collections.

Why are they interesting? Although these opals may not be as vibrant as the “classic” noble varieties, they hold great value for collectors. They are pieces of history, rare gemstones that cannot be found in every jewelry store.

As someone who loves opals, I always enjoy learning about such rare finds. Who knows, maybe interest in them will grow over time, and we will see them more often? For now, they remain hidden gemological treasures that are worth seeing at least once.

Olga Bachurina,
Co-Founder of Venus in Libra,
Certified by GIA & Gübelin Academy