Coloured stones
Blue sapphire — reading colour, origin and treatment
How Kanchanaburi, Ceylon and Kashmir sapphires differ, why the darkest stone in the tray is rarely the best buy, and what makes sapphire the most practical everyday gem.
Sapphire is the same mineral as ruby — corundum — differing only in the trace elements that colour it. Both sit at 9 on the Mohs scale, which is what makes sapphire genuinely practical for everyday wear.
Sapphire occurs in every colour except red, since red corundum is called ruby. This guide covers blue, still the most sought after.
What a good blue looks like
You want a saturated blue that is neither greyish nor blackened, and that stays bright indoors.
The mistake buyers make most often is picking the darkest stone in the tray because it reads as rich under display lights, then finding it looks like a dark spot in ordinary daylight. Always ask to see a stone in natural light, and tilt it through several angles.
Some sapphires suffer from extinction — patches that go dead and dark as the stone moves. The more extinction, the lower the value.
Origin and price
| Origin | Character | Price level |
|---|---|---|
| Kashmir | Velvety blue with a soft haze | Highest, extremely rare |
| Burma | Deep saturated blue | High |
| Ceylon (Sri Lanka) | Bright, lively blue | Medium to high |
| Bo Phloi, Kanchanaburi | Deep inky blue | Accessible |
| Madagascar | Highly variable | Medium |
Kanchanaburi sapphire has a signature deep, inky blue. Some stones run so dark they approach black, which is both its character and its limitation. Pick one that is deep but still alive and you get a stone that looks expensive for meaningfully less than Ceylon material.
In practice origin affects price more than beauty. If you are buying to wear rather than to invest, choose the colour you like first and ask where it came from second.
Ask this before you pay
Heating is routine and accepted, as with ruby. But there is a second treatment to watch for: diffusion, where colour is driven into the surface layer only. Recut or polish it deeply and the colour goes with it.
A report from GIT or another independent laboratory will state heated, unheated or diffusion-treated. Read that line every time.
Why sapphire suits an everyday ring
At hardness 9, only diamond and other corundum can scratch it. Most airborne dust sits around 7 on the scale, so it simply does not touch a sapphire.
Compare that with emerald at 7.5-8 and typically full of internal fractures — a stone you take off before housework. Sapphire needs no such care, and set in a bezel, with metal wrapping the girdle, it handles a working hand very comfortably.
Is a lighter or darker sapphire worth more
Neither by itself. The measure is saturation combined with brightness. A very dark, sleepy stone is worth less than a medium-toned one with vivid colour and life, so judge both qualities together.
Are other sapphire colours cheaper
Usually yes, with one exception: padparadscha, a pink-orange sapphire that is rarer and priced well above ordinary blue. Yellow, green and colourless sapphires are considerably more affordable and make excellent choices on a budget.
Can I tell a synthetic sapphire by eye
Not reliably — the material is chemically identical. The difference shows under magnification, where synthetics often display curved growth lines or round gas bubbles while natural stones carry crystal and needle inclusions. A laboratory report is the only certain answer.