Ceylon Star Sapphires

A torch will tell you most of it

A Ceylon star sapphire is the easiest stone we sell to fake convincingly and the easiest to check. Take it to one point of light, sunlight or a torch and move the light rather than your eyes.

A natural star drifts. The six rays glide across the dome as the light travels and the bright reflection of the bulb stays separate from the hub where the rays cross. On most synthetics the star and that reflection are welded together and slide as one piece. Look at the legs while you are there. On a natural star sapphire they are uneven, one ray brighter or longer or slightly bent, because the silk that made it grew that way. A star that is perfectly symmetrical, sitting on a body colour of even glassy blue, is telling you where it was made.

That test is not proof, which is why we put a report number on every stone. But it will save you from most of what is sold as star sapphire.

The silk that ruins a sapphire is the silk that makes this one

Roughly three quarters of the corundum that comes out of the Sri Lankan gravels is geuda: milky, translucent rough, clouded by rutile silk so dense the stones show a diesel sheen in transmitted light. Before the 1970s it was spread on garden paths. Then Thai burners worked out that heat dissolves the silk and the whole island's output of pale, useless rough became blue sapphire.

A star is that same silk, caught at the right density, in the right orientation, then left alone. Which is why heating and asterism cannot coexist. Burn a star sapphire and you get a cleaner, bluer stone with nothing on its face. So a deep, genuine star is itself reasonable evidence that a stone never went in the furnace and unheated is the ordinary condition at the good end of this category rather than a premium we charge you for.

Three ways to be sold a star sapphire that is not one

None of this is theoretical here. Coloured glass arrives in Sri Lanka by the kilo and leaves as souvenirs. The National Gem and Jewellery Authority has called it the biggest threat to the island's name. We publish a laboratory and a report number on every stone because of that, not in spite of it.

The star and the clarity are in competition

This is the judgement that decides what a star sapphire is worth and it pulls in two directions at once. Silk has to be dense enough to throw a bright, complete star. Push past that and the same needles kill the stone and you are left with a grey pebble wearing a good star. A cabochon that keeps some glow underneath a clean six ray star is the one worth paying for and we turn down a great deal more than we buy.

Then look at where the star sits. Centred on the dome, six rays reaching the edge rather than fading halfway. Dome height matters too. Too shallow and the star goes weak and diffuse. Too tall and the stone sits on the hand like a thumbnail. We watch our cutters orient these by eye against the crystal axis and a centred star on a well judged dome is the whole of that skill on show.

Silver blue is the Ceylon star sapphire signature

Sri Lanka and Burma are the classic sources for rutile stars. Ceylon material runs a soft silvery blue with a bright star, often closer to grey than to the saturated blue of a faceted stone. That silveriness is not a fault. It is what the silk does to the body colour and anyone selling you a star sapphire in vivid faceted blue is selling you something else.

Black star sapphire is a different animal. Its rays come from hematite rather than rutile, mostly in iron rich material out of Australia and Thailand. The stars are softer edged, the stones much cheaper. Stars turn up in pink and purple too. Yellow, orange and green are genuinely uncommon.

A star sapphire costs a fraction of a faceted stone

The market pays for transparency and a star cabochon has given most of that away to get its star. A fine faceted blue sapphire can run to several thousand dollars a carat and well beyond. A good star cabochon is more likely to sit in the hundreds to low thousands and size pushes the per carat price up far less steeply than it does on faceted goods.

That makes this the cheapest way into a large, certified Ceylon sapphire that nobody else will be wearing. The cabochon we have listed carries its own price and report. You can check the number with the laboratory before you commit to anything.

Living with a cabochon

Nine on the Mohs scale and no cleavage plane, the same as any sapphire, so it will not scratch or chip in normal wear. The dome does stand proud of a setting more than a faceted stone, so consider a bezel if the ring is going on a working hand.

Do not let anyone steam or ultrasonic a star stone without knowing its treatment history, because a glass filled cabochon will not survive it. Warm soapy water and a soft brush on a natural one. If a faceted stone was what you were really after, the same terms cover our blue sapphires, the rubies and everything else we list.