Something unusual happened in September at the Biennale des Antiquaires, the best fine art and antiques fair in the world, held in Paris every second year and featuring the most spectacular jewels from the haute joaillerie houses.

The “big four” gemstones – diamonds, emeralds, rubies and sapphires – have always dominated the show, but this year the name of the stone on everyone’s lips (and glinting in the showcases of Harry Winston, Cartier and Van Cleef & Arpels) was the Padparadsha sapphire. This is no ordinary sapphire. It is not even blue.