How should you assess an opal’s quality and value?

No two opals are the same. They can come in any colour, or combination of colours, and each one may differ considerably.

Because opals vary so much in appearance, they cannot all be assessed in the same way.

That’s why our gemmologist evaluates opals individually using five different quality factors: type, colour, clarity, cut and carat weight.

To fully appreciate an opal, our gemmologist recommends studying the gem under different kinds of lighting or against a dark background.

COLOUR

Opals can show one single colour. Or they can show a main “background colour” with additional “secondary colours”. For example, a white opal may have secondary colours that appear as flecks or pearl-like shimmer against a milky white background, depending on the individual stone. Fire opals on the other hand are valued for the uniformity of their main colour, ranging from yellow to orange, and they’re not expected to show any secondary colour or shimmer.

CARAT

Opals exist naturally in many different sizes. Opal size can be measured in carats, but it’s also commonly expressed in millimetre (mm) measurements. Some of the most common oval sizes are 6x4mm, 7x5mm and 8x6mm.

CLARITY

Transparency and clarity vary from opal to opal. Different degrees of clarity are valued in different types of stones. White opals are opaque and there is no expectation of glass-like transparency. A fire opal can vary from almost transparent to translucent. As with all gems, there may be impurities trapped in a stone, but inclusions or marks in white opals and fire opals should not be obvious to the naked eye.

CUT

Oval cuts are most commonly used in opals, because they maximise the use of the rough stone. An oval cut should always be symmetrical. White opals are most often polished into smooth, domed shapes called cabochons. This cut is the best for showing off their shimmer. Fire opals display the finest flashes of light when cut into facets.

Opal is generally untreated. However, as with all gems, enhancements and imitations can be found on the market.

In particular black opals are often treated with smoke or heat to enhance their black background colour.

Our gemmologist would recommend only buying opals that are not treated. A reputable jeweller will always declare if a stone has been enhanced, so that you can assess its true value.

Opal ranks 5 – 6.5 on the Mohs Scale of mineral hardness. This means that it is a gemstones of medium hardness and should be treated with care.

Avoid exposing opal to sudden, extreme temperature changes, because it can fracture.

The only safe way to clean opals is with warm water and soap, scrubbing gently with a soft toothbrush. Afterwards, rinse and pat dry with a clean cloth.

When wearing and storing opal jewellery, take great care not to knock or scratch it, as opal is quite a soft gem and can damage easily.

Opals were first set in European crown jewels by Napoleon Bonaparte. He gifted his wife, Empress Josephine, a superb red opal that had such fiery sparkle it was named “The Burning of Troy”.

In the late 1700’s opals fell out of fashion, until Queen Victoria revived their popularity. During her reign, vast opal fields were discovered in Australia and as the British monarchy was considered a leader in fashion at the time, opals were soon back in vogue.

Today, Australia’s biggest film star, Cate Blanchett, is a big fan of opals – not least because they are her country’s national gemstone. She famously wore opal earrings to the 2014 Oscars.

Photo: Joe Seer / Shutterstock.com

When Queen Elizabeth II visited Australia in 1953 after her coronation, the government of South Australia, famous for its opal fields, presented her with a necklace that had a large opal set into it. The gem was named the “Andamooka Opal”, after the town it was found in.

It’s believed to be the finest example of an Australian opal. It shows specks of colour in red, green and blue against a pale background and polished into an oval shape, it weighs 203 carats.

Famous lore surrounding the opal in Australia is an ancient indigenous story about the Creator of the Universe.

In this legend, the deity descended to Earth on a rainbow. Wherever he touched the ground with his feet, the stones began to shine in every imaginable colour. That is, according to the story, how opals were created.

Later on, when opals reached ancient Europe, people continued to believe they had magical powers. The Romans, for example, believed the gems could give their wearer good eyesight and help blonde women maintain their beautiful hair colour.