Few gemstones vary as dramatically from one specimen to another as opal.
One opal may display brilliant flashes of red, orange and green across a dark background. Another may appear almost transparent with delicate floating colours. A third may show predominantly blue and green. Others may display attractive body colour with little or no play-of-colour at all.
But appearance is only part of the buying decision.
A stone offered as opal might be a solid natural gemstone, a boulder opal retaining part of its host rock, or an assembled doublet or triplet. Some opals can be treated. Some are highly porous. Some can develop stability problems.
This makes opal an ideal gemstone for one simple buying principle:
Know exactly what you are looking at before comparing prices.
In this Opal Buying Guide, Lena Hoffmann explains the practical questions worth asking before purchasing an opal.
Table of Contents
1. Start With Play-of-Colour
For precious opal, play-of-colour is usually the characteristic that attracts attention first.
GIA identifies play-of-colour as the most important quality factor in precious opal.
But this does not mean simply counting how many colours appear in one photograph.
Look at the entire effect.
How bright are the colours?
How much of the visible surface shows play-of-colour?
Does the effect remain attractive as the stone moves?
Are there large areas where little or no colour appears?
Is the pattern visually interesting?
An opal does not need to show every colour of the rainbow to be beautiful.
A strong combination of two or three vivid colours can be much more attractive than a stone showing many weak colours.
Brightness and overall visual impact matter.
2. Move the Stone – Opal Should Not Be Judged From One Angle
Opal is a gemstone that rewards movement.
The colours that appear strongly from one direction can change, disappear or be replaced by other colours when the stone is tilted.
This is normal.
In fact, it is part of what makes precious opal so distinctive.
When buying in person, gently move the gemstone while observing the entire face.
When buying online, video can be considerably more useful than a single still photograph.
Ideally, you should see the actual opal moving under reasonably neutral illumination.
A photograph can capture one spectacular moment.
A video tells you much more about how the gemstone behaves.
3. Look at the Distribution of Play-of-Colour
Not all colour coverage is equal.
Some opals display bright play-of-colour across most of their visible surface.
Others contain strong colour in only a small area.
GIA describes areas where no play-of-colour appears as dead spots.
A limited dead area does not automatically make an opal undesirable.
But several large colourless areas can have a significant effect on its overall appearance.
Look at the stone as a complete composition.
Does your eye move naturally across the gemstone?
Or does one small flash of spectacular colour distract from a large area that otherwise appears inactive?
A good buying decision should be based on the entire opal rather than its best photograph.
4. Understand the Difference Between Body Colour and Play-of-Colour
An opal has more than one type of colour to consider.
Its body colour, sometimes called background colour, is the general appearance of the stone underneath the play-of-colour.
This can range from light or white through transparent or translucent material to grey or very dark backgrounds.
Play-of-colour is the shifting spectral colour visible within or across that background.
A dark body colour can create strong contrast and make play-of-colour appear especially vivid.
This is one reason fine black opal is so highly regarded.
But dark does not automatically mean superior.
Crystal opal can display spectacular colour while remaining transparent or semitransparent.
Fine white opal can also be exceptionally attractive.
Buy the visual combination you prefer rather than assuming there is only one correct type of opal.
5. Ask Whether It Is Precious Opal or Common Opal
Not every natural opal displays play-of-colour.
The distinction matters.
Precious opal displays play-of-colour.
Common opal does not.
Both can be natural and attractive materials.
Common opal can have beautiful body colours and can be desirable for jewellery, carving or collecting.
However, it should not be represented as though it possessed the same optical phenomenon as precious opal.
For consumers, this distinction becomes especially important when comparing prices.
Make sure you understand which type of opal is actually being offered.
6. Ask Whether the Opal Is Solid
This is one of the most important questions when purchasing opal.
A solid opal consists of opal throughout the gemstone.
But many attractive commercial opals are assembled from more than one material.
These are not necessarily poor products.
They simply belong to a different category and should be sold transparently.
Ask directly:
“Is this a solid opal or an assembled opal?”
Do not assume the answer from a face-up photograph.
From above, a well-made assembled opal can look extremely convincing.
7. Understand an Opal Doublet
An opal doublet generally consists of a thin layer of precious opal attached to a darker backing.
The dark backing can increase the apparent contrast of the play-of-colour and allows very thin opal material to be used attractively.
A good doublet can make beautiful jewellery.
There is nothing inherently wrong with purchasing one.
But it should not be priced or described as though the entire visible depth of the gemstone were solid precious opal.
GIA notes that assembled opals generally sell for only a fraction of the price of comparable solid material.
That is why disclosure matters.
You need to know what you are comparing.
8. Understand an Opal Triplet
A triplet takes the assembled construction one stage further.
A thin layer of precious opal is placed between a backing and a transparent upper cap.
The clear top can help protect the thin opal layer and magnify its appearance.
Again, a triplet can be attractive jewellery material.
But it is not commercially equivalent to a solid opal of the same visible dimensions.
The distinction is particularly important in online shopping, where the gemstone may only be shown face-up.
If the product description does not clearly state whether an opal is solid, doublet or triplet, ask.
Transparency should not depend on the buyer already knowing how to identify the construction.
9. Examine the Stone From the Side and Back When Possible
One of the easiest ways to understand an opal is to look at more than its face.
Side and back photographs can reveal information that is almost invisible from above.
With a doublet, you may be able to see the boundary between the precious opal layer and its backing.
With a triplet, the layered construction may be visible from the side.
Boulder opal, by contrast, naturally retains host rock as part of the stone.
That is not an artificial backing.
It is part of the natural material from which the opal formed.
The visual distinction matters because these are fundamentally different products.
For important online purchases, request photographs of the sides and back as well as the face.
10. Do Not Confuse Boulder Opal With a Doublet
Boulder opal can naturally contain precious opal within or attached to its host rock.
The host rock is intentionally retained during cutting.
That differs fundamentally from a doublet, where a separate backing has been attached to the opal.
A boulder opal can therefore display visible brown or dark host rock while still being a completely natural, non-assembled gemstone.
This is a good example of why simply seeing dark material underneath an opal does not tell you everything.
Ask what type of opal you are buying.
Correct terminology is more reliable than assumptions.
11. Look Carefully for Crazing
One of the most important condition issues in opal is crazing.
Crazing is a network of fine cracks that can develop within the gemstone.
GIA explains that moisture loss, excessive dryness, heat or intense light can contribute to crazing in susceptible material.
A crazed opal should not be confused with an ordinary play-of-colour pattern.
Look carefully.
Fine fractures may appear as irregular lines or a network running through the material.
Crazing is not merely cosmetic.
It can significantly reduce durability.
For an expensive opal, visible cracking deserves serious consideration before purchase.
12. Other Fractures and Surface Damage Matter Too
Not every crack in opal is crazing.
An opal can also contain individual fractures, chips, pits or other surface imperfections.
Look carefully around the edges of a cabochon, particularly where it would meet a jewellery setting.
Check the polish.
Look for obvious chips or fractures.
If the stone is already mounted, examine exposed areas carefully.
One small natural characteristic may have little practical importance.
A large fracture extending through the stone is a different matter.
The important question is whether a feature affects appearance, stability or safe use.
13. Ask About Treatment
Opal can undergo several forms of treatment.
According to GIA, treatments can include impregnation with substances such as oil, wax or plastic, as well as surface or colour modifications.
Other documented treatments include smoke treatment and sugar treatment.
These procedures can change colour, appearance or apparent clarity.
Treatment is therefore not a minor technical detail.
It can materially change what the consumer sees.
Ask:
“Has this opal been treated, and if so, how?”
The answer should be clear.
CIBJO’s gemstone standards likewise require accurate disclosure of gemstone treatments throughout the jewellery trade.
14. Dark Opal Deserves a Treatment Question
A dark background can make play-of-colour appear particularly vivid.
Natural black opal exists and can be highly desirable.
But dark body colour can also sometimes be created artificially.
GIA has documented smoke treatment, sugar-acid treatment and dyeing in porous opal material.
This does not mean every dark opal should be regarded with suspicion.
It means that colour treatment becomes a relevant question when significant value is being placed on the dark appearance of the gemstone.
For an important purchase, independent gemmological testing can help distinguish natural characteristics from detectable treatment.
15. Understand Hydrophane Opal
One term consumers increasingly encounter is hydrophane opal.
Hydrophane opal is porous enough to absorb liquids.
GIA’s research into Ethiopian deposits has shown that much Ethiopian opal is hydrophane.
When water enters this porous structure, the appearance of the stone can temporarily change.
Transparency can change.
Play-of-colour can appear different.
Even the weight can temporarily change.
Not all Ethiopian opal reacts in exactly the same way, because porosity varies between stones.
Hydrophane behaviour is therefore not automatically a defect.
But it is something the owner should understand.
16. Do Not Perform Home Water-Immersion Tests
You may encounter online advice suggesting that Ethiopian opal should simply be placed in water to determine whether it is hydrophane.
That is not a sensible experiment for an important gemstone.
GIA has documented durability concerns associated with immersing some hydrophane opals.
Existing small cracks can potentially worsen.
For that reason, professional gemmological identification is preferable to experimenting on the stone yourself.
If knowing whether the opal is hydrophane matters to your purchase, ask the seller or use appropriate professional examination.
A buying guide should help you protect a gemstone, not encourage potentially damaging home tests.
17. Ethiopian Opal and Australian Opal Should Not Be Reduced to “Better” and “Worse”
Australia has an extraordinary history of producing fine opal.
Ethiopia has also become an important source of beautiful precious opal.
The materials can have different characteristics, but the country name alone does not determine quality.
GIA specifically states that opal value is based on quality rather than simply where the gemstone was mined.
A fine Ethiopian opal can be far more visually attractive than an ordinary Australian opal.
A fine Australian black opal can occupy a completely different market position again.
Evaluate the individual stone.
Then consider geographic origin as additional information.
Do not substitute origin for quality.
18. Photographing Opal Is Especially Difficult
Opal can be one of the most challenging gemstones to represent accurately online.
The play-of-colour depends heavily on angle and illumination.
A photographer can position an opal at precisely the angle where its strongest colours appear.
That photograph may be genuine.
But it may not represent what the stone looks like from every angle.
Background matters too.
A dark background can increase perceived contrast.
Strong directional lighting can produce spectacular flashes.
This is why a responsible online presentation should ideally include several photographs and video.
Ask yourself:
Does the opal look attractive only in one carefully selected frame?
Or does the colour remain interesting while the stone moves?
The second question is far more useful to a buyer.
19. Compare Opals Under Consistent Lighting
Comparing two opals photographed under completely different conditions tells you very little.
One may have been photographed under powerful directional light.
Another under soft ambient lighting.
If possible, compare stones under similar conditions.
When buying in person, place the stones together.
Rotate them slowly.
Observe how much of each surface shows play-of-colour.
Look at brightness, pattern and coverage.
Then choose according to overall appearance rather than one spectacular colour flash.
Comparison is particularly valuable with opal because no two stones are exactly alike.
20. Consider the Cut and Dome
Opal is commonly cut as a cabochon rather than faceted.
The shape and dome influence how effectively play-of-colour is presented.
GIA notes that domed surfaces can help produce attractive play-of-colour from a range of viewing angles.
Look at the overall symmetry.
Check the polish.
Look at whether the dome feels proportionate to the gemstone.
An extremely flat opal can also be more vulnerable in some jewellery settings.
A very high dome may create its own setting challenges.
Cut should support both beauty and practical use.
21. Bigger Does Not Automatically Mean Better
Opal can occur in relatively large sizes.
That can make carat weight tempting as a simple comparison tool.
But two opals with identical weight can differ dramatically in desirability.
One might show vivid play-of-colour across almost the entire surface.
Another might display only weak colour in a small area.
One may have an attractive pattern.
Another may have significant dead spots.
One may be stable and intact.
Another may contain cracks.
Weight is therefore only one piece of information.
Buy the opal, not the number on the scale.
22. Think About How You Intend to Wear It
Opal is beautiful jewellery material, but it deserves thoughtful care.
GIA advises that opal is more vulnerable to scratching, chipping and breaking than many gemstones commonly used for jewellery.
That does not mean opal should never be worn in a ring.
It means the setting and lifestyle matter.
A protective bezel or surrounding metal can provide additional protection.
Earrings and pendants generally receive fewer direct knocks than frequently worn rings.
If you want an opal ring for daily wear, consider how active you are with your hands.
The best gemstone purchase is one that suits how you intend to use it.
23. Care Depends on What Type of Opal You Own
There is no benefit in knowing that a gemstone is an opal while ignoring whether it is solid, assembled, hydrophane or treated.
These details can influence care.
GIA advises warm soapy water as the general safe cleaning method for opal.
However, prolonged immersion deserves additional caution.
Water can affect adhesives used in doublets and triplets.
Hydrophane opal can absorb liquid.
High heat and sudden temperature changes should also be avoided.
Ultrasonic and aggressive cleaning methods are not appropriate choices for opal.
When purchasing the gemstone, ask for care advice that applies to the specific type of opal you are buying.
24. Understand What a Laboratory Report Can Tell You
For an important opal purchase, an independent laboratory report can provide useful information.
GIA states that it evaluates opal but does not assign it an overall quality grade.
A GIA Colored Stone Identification Report can identify whether material is natural or laboratory-grown and report detectable treatments.
This distinction matters.
The laboratory can help answer:
What is this material?
Is it natural?
Is treatment detectable?
But the laboratory does not decide whether you should find the pattern beautiful.
It does not replace your personal judgement of play-of-colour.
Identification and appreciation are different things.
25. Do Not Rely on AAA or Similar Grades Alone
As with many coloured gemstones, sellers may use proprietary terms such as:
AAA,
AAAA,
premium,
top quality,
museum grade,
investment grade,
or collector grade.
These can form part of an internal commercial evaluation system.
But they should never replace a description of the actual opal.
Ask what the designation means.
Does it refer to play-of-colour intensity?
Pattern?
Body colour?
Colour coverage?
Condition?
Treatment?
Construction?
A label becomes useful only when its meaning is explained.
The gemstone should remain the evidence.
26. Ask Why One Opal Costs More Than Another
Opal pricing can initially seem confusing because superficially similar stones may have dramatically different prices.
There can be legitimate reasons.
One may be solid while another is a triplet.
One may have much stronger play-of-colour.
One may display desirable colour across almost its entire surface.
One may have a particularly attractive pattern.
One may possess a highly desirable dark natural background.
One may be treated.
Another may contain crazing.
One may simply offer a far stronger overall visual experience.
When the price difference is substantial, ask the seller to explain it.
A premium should be supported by meaningful characteristics rather than adjectives alone.
27. Look for a Seller Who Clearly States What the Opal Is
Transparency is especially important with opal because so many different products can appear visually similar from above.
Before purchasing, you should ideally know:
whether the opal is natural or synthetic,
whether it is precious or common opal,
whether it is solid, boulder, doublet or triplet,
whether treatments are known or detected,
whether hydrophane behaviour is relevant,
whether cracks or stability issues are present,
whether the images show the actual gemstone,
and what care the stone requires.
A responsible description makes these differences easier to understand.
The buyer should not need specialist expertise simply to determine what category of product is being sold.
The NGB Buying Principle
Opal is not a gemstone that should be reduced to carat weight or the number of colours visible in one photograph.
Its beauty depends on movement.
Its value can depend on the intensity, coverage and pattern of its play-of-colour.
Its construction matters.
A solid opal, boulder opal, doublet and triplet are different products.
Treatment matters.
Stability matters.
Hydrophane behaviour can matter.
And online presentation matters enormously because the gemstone can look different with every change of angle and illumination.
The strongest purchase is therefore not necessarily the opal that produces the most dramatic single photograph.
It is the opal whose appearance you genuinely love — and whose identity, construction, treatment, condition and care requirements you understand.
Buy the stone you love — but understand the stone you buy.
References & Further Reading
Gemological Institute of America (GIA) — Opal Buyer’s Guide
Consumer-oriented guidance covering play-of-colour, clarity, cut, assembled opals, durability, treatments and purchasing considerations.
https://www.gia.edu/opal/buyers-guide
Gemological Institute of America (GIA) — Opal Quality Factors
Detailed educational information about body colour, play-of-colour, pattern, transparency, crazing, cut and the construction of opal doublets and triplets.
https://www.gia.edu/opal-quality-factor
Gemological Institute of America (GIA) — Opal Care and Cleaning Guide
Guidance concerning opal durability, crazing, heat exposure, treatments and appropriate cleaning methods.
https://www.gia.edu/opal-care-cleaning
Gemological Institute of America (GIA) — Does GIA Grade Opal?
Explanation that GIA evaluates but does not assign an overall quality grade to opal, and information about Colored Stone Identification Reports.
https://www.gia.edu/FAQ/gia-faq-grade-opal
GIA Gems & Gemology — A Useful Technique to Confirm the Hydrophane Nature of Opal
Professional gemmological discussion of hydrophane opal, water absorption and potential durability concerns associated with immersion.
https://www.gia.edu/gems-gemology/fa13-ln-technique-hydrophane-opal
GIA Gems & Gemology — Land of Origins: A Gemological Expedition to Ethiopia
Research covering Ethiopian opal deposits and the hydrophane behaviour of much of the material from these deposits.
https://origin.prod.author.gia.edu/gems-gemology/spring-2019-land-of-origins-gemological-expedition-ethiopia
CIBJO – The World Jewellery Confederation — Industry Standards Resources
Current CIBJO standards and gemstone guidelines, including the dedicated Opal Guide and the Gemstone Blue Book.
https://cibjo.org/industry-standards-resources/
CIBJO – The World Jewellery Confederation — Opal Guide Announcement
Information concerning CIBJO’s dedicated Opal Guide and its internationally agreed terminology for the wide range of natural and artificial opal products.
https://cibjo.org/cibjo-coloured-stone-commission-presents-newly-released-opal-guide/
CIBJO – The World Jewellery Confederation — Do’s & Don’ts Guide
Current consumer and retailer guidance concerning transparent descriptions, treatments, artificial products and responsible gemstone disclosure.
https://cibjo.org/dos-donts-guide/
