How to read a gemstone report

The trade says certificate. The laboratories say report, and they are careful about it, because a certificate implies a guarantee and what a laboratory issues is the considered opinion of named gemmologists on the day they examined the stone. The distinction sounds pedantic until the day two respected laboratories disagree about the same stone, which happens, and which the vocabulary of certification has no way to describe.

The reports that carry weight internationally come from a short list: the Gemological Institute of America; SSEF, the Swiss Gemmological Institute in Basel; the Gübelin Gem Lab in Lucerne; AGL in New York; and, for coloured stones, GRS. For a significant coloured stone, a report from one of the Swiss laboratories is often what the market expects.

Species and variety

The report names the mineral species first, then the variety. Corundum is the species; ruby and sapphire are varieties of it, separated only by colour. Beryl is the species; emerald, aquamarine and morganite are varieties of it. The distinction matters commercially because the boundary between a pink sapphire and a ruby is a judgement about saturation, and it is a judgement worth a great deal of money.

Weight and measurement

Weight is given in carats, and one carat is exactly two hundred milligrams — a unit of mass, not of size, and not to be confused with the karat that measures gold purity. Measurements are given in millimetres. Together these are how you confirm that the stone in front of you is the stone the report describes: take the weight and the three dimensions, and check them against the paper before anything else.

Colour

For most coloured stones a laboratory describes rather than grades. You will read something like “vivid blue” or “intense red”, which is a controlled description arrived at under standard lighting, not a position on a universal scale of the kind diamonds have.

Some laboratories will additionally apply a trade appellation — pigeon's blood for a certain red in ruby, royal blue for a certain blue in sapphire. These are honoured names and they carry a premium. They are also thresholds set by each laboratory according to its own criteria, which is why a stone may earn the appellation from one house and not from another. Treat them as a strong opinion, expertly given, rather than as a measurement.

Treatment: the first line that moves the price

This is the section to read first, and the one a seller is least likely to volunteer.

Heat

Long-established, stable, permanent and applied to the great majority of sapphire and ruby on the market. It is fully accepted, and it must still be disclosed. An unheated stone of fine colour commands a substantial premium precisely because it is uncommon — which is why “no indications of heating” is one of the most valuable sentences a report can contain.

Diffusion

Colour introduced into the stone's surface layer, or into its lattice, by an element added during heating — titanium, or beryllium. This is a different order of intervention from heat alone, and it reduces value sharply. It must be disclosed and named.

Clarity enhancement in emerald

Oil or resin drawn into surface-reaching fractures to make them less visible. Near-universal, and graded by degree — commonly none, minor, moderate or significant. The degree matters: it tells you how much of what you are seeing is the stone and how much is the filler, and it dictates how the piece must be cleaned for the rest of its life.

Lead-glass filling in ruby

Fractured low-grade material impregnated with high-refractive-index glass, producing a stone that looks far better than the corundum inside it. Often described in the market as composite ruby. It is fragile, it can be damaged by ordinary jeweller's work, and it is worth a small fraction of an untreated stone of the same appearance. A report will say so.

Origin: the second line, and an opinion

Many reports on significant coloured stones offer a country of origin. It is arrived at by comparing the stone's trace-element chemistry and the scene of its inclusions against the laboratory's own reference collection of stones of known provenance, built over decades. It is skilled work and it is not a measurement.

Origin can be worth as much as everything else on the page combined. A sapphire attributed to Kashmir, a ruby to Mogok in Burma, an emerald to the Colombian mines — each attribution carries a premium far beyond what the stone's appearance alone would support. Where deposits overlap geologically, laboratories can and do reach different conclusions, and the honest ones will say that the data was inconclusive rather than choose. A report that declines to state an origin is not a weaker report. It is often a more careful one.

What the report does not tell you

• What the stone is worth. No reputable laboratory values stones; a report and an appraisal are different documents, produced by different parties, for different purposes.
• Whether it is beautiful. Two stones with near-identical reports can be separated by a wide margin in the hand, and the margin is the reason to see a stone before agreeing to it.
• Whether the stone was mined and traded responsibly. That is a supply-chain question and it travels on different paper.
• Anything about the setting, the workmanship, or the house that made it.

Checking that the report is real

1. Enter the report number in the issuing laboratory's own online verification service, reached by typing the laboratory's address yourself rather than by following a link or a code printed on the document.
2. Match the weight and all three measurements against the stone, not only the weight.
3. Check the date. A report from many years ago describes a stone that may since have been recut, re-treated or replaced, and origin methodology has moved on. For a significant purchase, ask for a current report.
4. Read the comments section at the foot. Qualifications that matter are frequently placed there rather than in the body.
5. Be wary of a report from a laboratory you cannot find an independent account of. The names above earned their standing over decades, and the standing is the product.

How the House uses them

Every SINGULLUM Creation is delivered with the independent report for its stone, alongside the record of where the stone was acquired, the metal it is set in, and the date the design was retired. The House states the treatment whatever it is, and states nothing about origin that a laboratory or the chain of supply cannot support. How we buy is set out under responsible sourcing.

Written to inform. It is not a valuation, an appraisal, or advice on a purchase or an investment, and it does not speak for any laboratory named in it.