Aluminium was once worth more than gold. In the 1880s, builders capped the Washington Monument with a small pyramid of aluminium, then a rare metal. Today, the base metal is used in cars, planes and cans. The price, sensitive to economic growth, has taken a knock this year and is down 11 per cent. Traders have found a profitable opportunity to buy up supply. But do not expect the same sort of supply squeeze experienced in 2013.

Back then, the warehouses of the London Metal Exchange, owned by Hong Kong Exchanges and Clearing, were blamed for a logjam. Traders who see low prices can purchase metal, store it in warehouses and sell contracts for future delivery, thereby locking in profits. In 2013, aluminium flowed into storage easily enough. But an overly complicated system of queueing to remove metal from LME warehouses encouraged traders to game the system. LME warehouses collecting storage fees did not help. By August 2014, the aluminium price had rallied as much 17 per cent. Fingers were pointed at the LME.

Changes to the system have since followed. More importantly, LME warehouses have grown less popular. Warehouses outside the systems of the largest exchanges, LME and Shanghai, have attracted more aluminium stock in the past few months. Financing and storing aluminium delivered a return of around 4 per cent this spring, the most in six years. A certain sheen has returned to the grey metal.