A 175-Year Commodity Market Rule Is Starting to Break

In commodity markets, certain truths can be taken as self-evident. Gold consistently cost about 15 times as much as silver for more than 2,000 years, from the time of the Lydian king Croesus to the 19th-century gold standard. Sharp movements in the ratio between copper and oil prices are often taken by traders as indicators of seismic shifts in the world economy.