From base to gold

WHEN Marco Polo travelled to China in the 13th century, he found that among its wonders was “the secret of the alchemists”. Its imperial court could turn mulberry bark into money. It simply printed paper notes, decreed that people must accept them and killed counterfeiters. For a Venetian used to gold coins, the world’s first fiat currency was a marvel. Its value derived not from precious metal but from the credibility of the regime issuing it. This month China achieved another kind of monetary alchemy: to fashion a global reserve currency out of one that, by a range of criteria, does not yet merit such status.