Big Bezel Ruby

Ruby is corundum, the same mineral as sapphire, coloured red by chromium. The chromium does a second thing: it makes the stone fluoresce, so a fine ruby glows red even in daylight, the lit-from-within quality the best are known for. At 9 on the Mohs scale it is hard enough to be worn every day, for generations.

In Sanskrit ruby was ratnaraj, the king of precious stones. For centuries the reds of Burma set the standard, and pigeon's blood, the trade's name for the finest of them, is still the phrase every red is measured against. Many of history's famous rubies have turned out to be spinel, the Black Prince's Ruby in the British crown among them.

Ruby is found in Myanmar, whose Mogok valley is the historic source; in Mozambique, one of the largest sources since 2009; and in Thailand, Cambodia, Sri Lanka, Madagascar, Tanzania and Vietnam, each its own shade of red.

Burma's rubies come from Mogok, a valley in the hills of the north, worked for centuries, where by law the largest stones once belonged to the king. They grew in marble, which holds almost no iron, so nothing damps the chromium's fluorescence: a Mogok ruby glows. The finest are the pigeon's blood reds the trade measures every other ruby against.

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Take it off for the gym, the sea and the garden. Warm water, a drop of soap and a soft brush; dry with a soft cloth.