Coloured stones: sapphire, emerald and ruby

Why colour is having its moment

Great coloured stones are rarer than great diamonds, and the market has noticed. A top Kashmir sapphire, a Burmese ruby with pigeon-blood colour or a Colombian emerald with that particular bluish green can now fetch more per carat than any white diamond. For the private buyer, the interesting news is at the level below the record books: a fine two-carat Ceylon sapphire still costs less than a one-carat D flawless diamond and is, to most eyes, the more beautiful object.

Sapphire

Sapphire is corundum, and it comes in every colour except red. The classic is a medium to deep velvety blue with strong saturation. Ceylon (Sri Lanka) stones are bright and lively, Madagascar stones can match them, Kashmir stones are the legend and priced like one. Pink, padparadscha (a pink-orange), yellow and teal sapphires are the modern connoisseur’s choice and often much better value. Sapphire scores nine on the Mohs scale, so it is perfectly happy in a ring worn every day.

Ruby

Ruby is red corundum, and the finest colour is a pure, slightly bluish red with high saturation. Burma (Myanmar) is the benchmark origin; Mozambique now produces superb stones at a fraction of the price. Almost all rubies are heated to improve colour and clarity. That is accepted and disclosed; what you want to avoid is glass-filled ruby, which is a composite and should be priced as one.

Emerald

Emerald is beryl coloured by chromium and vanadium. Colombian stones show a warm, slightly bluish green; Zambian stones are a cooler, deeper green and often cleaner. Nearly every emerald has fissures that are filled with oil or resin to improve appearance. Minor oil is normal; the laboratory report states the degree. Emerald is softer (7.5 to 8) and brittle, so a ring needs a protective setting and a little respect.

Origin, treatment, report

For any coloured stone above a few thousand dollars, ask for a report from Gübelin, SSEF, GRS or AGL. These laboratories state the origin and any treatment. An unheated Ceylon sapphire or an emerald with only minor oil carries a premium because it is rare. That premium is real and it survives resale.

How to look at a stone

Look at it in daylight, in the shade, under a warm lamp and at arm’s length. A great stone keeps its colour when you move it; a lesser stone goes dark in the shade or washes out in the sun. Ignore the loupe until you have done that. Colour first, then cut, then clarity, then size.