Natural imperfections in opal, explained
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Why natural opal isn't uniform
Opal forms in sedimentary rock over millions of years, growing inside seams of sandstone or ironstone alongside plain potch (opal with no play-of-color), sand, and trace minerals. A natural stone carries some trace of where it came from; a lab-grown one doesn't, because it was never in the ground at all.
That's the trade: a solid natural opal will show some character from its formation. It's the same reason no two are ever identical, and the reason each of ours gets a name instead of a style number.
Potch, and the word worth learning
Potch is opal without play-of-color. Same material, same silica, but the spheres inside didn't stack regularly enough to diffract light, so it comes out as plain grey, white, amber or black glassy stone. It is the overwhelming majority of what any opal field produces — a miner brings up a bucket of potch for every stone worth cutting.
Black potch matters to a buyer for two reasons. First, it's the natural backing behind the colour bar in a Lightning Ridge black opal — the thing that makes a black opal black. Second, it's what a doublet backing is frequently cut from, glued behind a thin slice of colour to imitate exactly that effect. Same material, honestly used in one case and to fake a solid stone in the other. Knowing the word means you can ask which one you're looking at.
Potch lines and patches inside a solid stone are normal, and often beautiful. A clean division between colour and potch is just the edge of where the good ground stopped.
What's normal, and what's boulder opal on purpose
Small potch patches, faint sand inclusions, and fine natural fissures within the color bar are common and don't affect how a stone wears. Our cutter checks every stone before it's cut and again before it's sold; if a feature could compromise the stone, it doesn't leave the bench.
Boulder opal is different again: the ironstone matrix is left on the back of the stone deliberately, not hidden or removed. It's what gives boulder opal its earthy color and a lower price than an equivalent solid crystal or black opal, and it's stated plainly on the certificate as 'boulder opal', never passed off as something else.
A matrix opal ring, a boulder matrix pendant, a Koroit stone webbed with ironstone through the face — those are all the same idea, and in every case the dark material is host rock rather than a glued-on backing. That distinction is the entire difference between boulder opal and a doublet, and it's set out at length on the boulder opal page.
When an inclusion is actually a problem
Crazing — a fine network of cracks through the body of the stone — is the real fault, and it's a reason a stone never gets cut, let alone sold. It's mostly a hydrophane problem rather than an Australian one. A fissure that runs through the colour bar and could open under pressure is the other one.
Everything else is character. An honest inclusion is not a defect, and I won't sell a stone I wouldn't wear myself — but I also won't apologise for a stone looking like it came out of the ground, because that's the whole point of it.
From Opalani
Every certificate states exactly what you're holding: solid natural opal, with any matrix noted, never a doublet or triplet standing in to hide a flaw.
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