A rare pink diamond is the ultimate limited edition. The most sought-after pink diamonds in the world fetch prices of up to 50 times higher than white diamonds. Each one might be the size of a pea – the largest ones rarely exceed two carats – but they regularly top $1million a carat. These tiny objects of beauty – and of nature – have a history of defying the recession. In 2010, diamond mogul Laurence Graff bought a pink diamond at Sotheby’s for a staggering $45.6million, breaking all previous records for a gem sold at auction. “Acquiring pink diamonds is about incomparability,” says Robert Procop, private jeweller to Angelina Jolie. “The concern for rarity and personality that lies behind the rise of pink diamonds is typical of an art collector’s attitude.” It should therefore come as no surprise that when I attended a one-day exhibition of highly-prized pink diamond jewellery at The Orangery in Kensington Palace, hosted by Argyle, which controls 90 per cent of the world’s pink diamonds through its Rio Tinto-owned mine, security was on high alert.