Why opal doesn't work like diamond
Diamond has a system: cut, colour, clarity, carat, and laboratories that will put a grade on a certificate. Opal has none of that. There is no universally accepted opal grading scale, and no certificate that will tell you whether one stone is worth more than another.
That is not a gap in the market so much as a fact of the stone. Two opals cut from the same rough can look like strangers. Value comes down to four things you can see with your own eyes — which is good news, once you know what you are looking at.
The four things, in order
- Brightness. How much light the stone throws back at you. The trade uses a rough scale from 1 to 5; a stone at the top of it reads from across a room. This is the factor that matters most and photographs worst, which is exactly why it is where beginners get taken.
- Pattern. The shape the colour takes. Harlequin — a mosaic of angular, close-fitting patches — is the rarest and the most valuable. Broad or rolling flash is a wide sheet of colour that moves as you tilt the stone. Pinfire is made of tiny points. Between them sit floral, ribbon and straw patterns. A well-defined pattern beats a busy one of the same brightness.
- Body tone. The darkness of the stone's background, graded N1 (near-black) to N9 (very light). This is the only part of opal that has a formal scale, and its effect is simple: a darker background makes the play-of-colour read as brighter.
- Size and cut. Opal is sold by carat, and price rises steeply with size — a large stone of ordinary brightness can cost more than a small spectacular one. Cut is almost always a cabochon: look for a smooth, regular dome with no flat spots, and no sand or potch breaking the face.
Brightness matters most and photographs worst. Ask for video, not stills.
The five questions to ask before you pay
- Can I see it on video, in daylight, turning slowly? Play-of-colour changes with angle. A single still photograph can make a dull stone look extraordinary, or hide a dead spot on one side.
- Is it solid, or a doublet or triplet? Assembled stones are a thin layer of opal glued to a backing, sometimes capped with quartz or glass. They are legitimate and much cheaper — but they must be disclosed, and they should never be priced as solid opal.
- Has it been treated? Sugar-and-acid darkening is routine on some matrix opal, and smoking and resin filling also exist. Treating is not automatically a problem, but it changes both durability and price, and you are entitled to know.
- Where is it from? Australian and Ethiopian opal behave differently in wear — Ethiopian material is often hydrophane, meaning it takes on water. We cover what that means for you in is opal durable enough for everyday wear.
- Is there a photograph on a neutral background? Opal is usually shot on black because it flatters the colour. Ask for plain grey or white — it is the honest test of brightness.
Red flags
- Black opal at a black-opal-impossible price. Black opal comes from essentially one place on earth and is the scarcest opal there is. When it is cheap, it is usually a dark-treated stone, a doublet, or not opal.
- “Genuine opal” and nothing else. “Genuine” has no fixed meaning in most markets. Ask what the stone is, where it came from, and whether it has been treated.
- A flash that looks the same from every angle. Glass and resin imitations, and laboratory-grown opal, tend to show a very regular, column-like sheen rather than an irregular organic pattern.
- A seller who will not send a video. There is no innocent explanation for this one.
What you are really paying for
Once a stone is in a piece of jewellery, matching matters as much as grading. The setting has to suit that specific stone — its height, its outline, how much of the face the metal covers. A stone cut for a generic calibrated size is convenient; a stone chosen first, with the setting built around it, is a different object.
If it is your first opal: a bright white or crystal opal in a pendant is the best value there is. Black opal and boulder opal are where the money goes, and both are worth waiting for.
The checklist, on one page
- Brightness first, then pattern, then body tone, then size.
- Video, in daylight, stone turning. Never buy from a single still.
- Confirm three things: solid or assembled, treated or untreated, and origin.
- Ask for a neutral background and no retouching.
- Make sure the exact stone you are shown is the stone that arrives.