Ageing of metal surfaces

Outdoors, bare copper loses its shine within days and turns chestnut brown in the first year. Surfaces patinated in the workshop keep their colour; indoors it stays almost unchanged for years.

Outdoors the brown keeps darkening, on vertical façades to an anthracite brown that usually remains the final state. On pitched roofs, where rain lingers, the shift towards green begins, much earlier on the coast than in the city.

The Sinclair Tower in Vancouver (image right) dates from 2004. Today the dome shows the full green of the carbonate layer, a surface whose development can be traced across two decades.