Glass-Filled Ruby and Other Traps for the Unwary Buyer

Nobody sells a fake ruby. They sell a real piece of corundum, or glass, or laboratory-grown crystal, and attach to it a word it has not earned: natural, unheated, Burmese, Mogok, pigeon’s blood. The stone is rarely the problem. The label is. These are the five traps I see most often, what each one is, how it is caught, and why the laboratory report is the only defence that does not depend on the seller’s character.

Lead-glass composite ruby

Around the middle of the 2000s the market filled with large, bright red stones at prices that made no sense. They were low-grade corundum from Africa, heavily fractured and nearly opaque, that had been cleaned, fractured further and filled with high-lead glass until they looked like ruby. The glass carries the light; the corundum carries the name. Under a loupe the filler shows trapped gas bubbles, flow structures like frozen syrup, and a blue or orange flash where glass meets stone. A jeweller’s torch softens the glass; household acids and even lemon juice etch it. A composite of this kind is not a treated ruby. It is a manufactured object, and serious laboratories describe it as such. The first tell is the price: a five-carat red stone offered at the price of a dinner is not a bargain, it is glass.

Flux-healed and heavily heated stones

Heat is honest work when it is declared, and most corundum on the market has been to a furnace. The trap is the second step. Ruby from Mong Hsu in Burma and some African material is heated with a flux that melts into the fractures and heals them, leaving glassy residues in the fissures. A stone healed that way is sold as heated, or worse, as unheated, and the price paid is for a stone that does not exist. The treatment line on a report from Gübelin, SSEF, GIA or AGL will say whether there are indications of heating and whether residues are present in healed fissures. The unheated premium is real precisely because the word is so easily attached to the wrong stone.

Beryllium-diffused sapphire

Early this century the trade was flooded with padparadscha-coloured and orange sapphires that turned out to have been heated with beryllium, which diffuses into the lattice and changes the colour from the outside in. The result can be beautiful and it is a legitimate product when disclosed, but it is not a natural-colour padparadscha and it should never carry that price. Diffusion is detectable, sometimes only by advanced testing, which is one more reason the top of the market sends every stone to a house with the equipment. The same logic applies to titanium-diffused blue and to every new treatment that arrives: it is fine when it is on the paper, and fraud when it is not.

Synthetics sold as natural

Flame-fusion ruby has been grown since 1902, flux-grown and hydrothermal crystals since the middle of the last century, and emerald has been grown in laboratories for decades. Honest synthetics are sold as synthetics at a fraction of the natural price. The trap is the crystal that arrives in a parcel in a market town with a story about a mine, or in a piece of old jewellery whose owner believes the family legend. Identity is the first line on a report because it is the first thing that can be faked, and a loupe in daylight catches many synthetics through their growth features. It does not catch all of them. The laboratory does.

Certificates from nowhere

The fifth trap is paper. A stone arrives with a certificate: a crest, a hologram, a laboratory name you have never heard of, a colour appellation in bold. Some of these houses are small and honest and simply unknown. Many exist to print what the seller pays for. The test is simple: can you verify the report number on the laboratory’s own website, and does the trade you will one day sell into accept that name. For anything at the top of the market the answer has to be Gübelin, SSEF, GIA or AGL, and reading their reports properly is the skill that makes the rest of this note unnecessary.

The defence

Never buy on the seller’s word, never buy in the seller’s light, and never pay before a laboratory of your choosing has described the stone in your own name. The sequence of due diligence exists because every trap above defeats the eye at least some of the time, including mine. The stone will tell the laboratory what it is. Your job is to make sure the laboratory is asked before the money moves, and that the answer is written on paper the whole trade can read.

Buy the stone, then read the paper. Never in the other order.

Questions collectors ask

How do I know if a ruby is glass filled?

Under magnification a lead-glass composite shows gas bubbles trapped in the filler, flow structures like frozen syrup, and a blue or orange flash where the glass meets the corundum. It is often sold at a price no natural ruby of that size could carry, which is the first tell. A laboratory report from a serious house states the treatment plainly; the absence of such a report on a cheap large ruby is the report.

Is a heated ruby a fraud?

No. Heat treatment is honest work when it is declared, and most ruby and sapphire on the market has been heated. The fraud is a heated stone sold as unheated, or a flux-healed stone sold as merely heated. The treatment line on a report exists to separate those cases, and it is the line to read first.

Are synthetic rubies worthless?

Not worthless; they are a different product with a different price, sold honestly by laboratories that grow them. The damage is done when a synthetic is sold as natural, which still happens in every gem market in the world. Identity is the first line on a laboratory report because it is the first thing that can be faked.