Empire of dust: what the tiniest specks reveal about the world

For two centuries, London’s buildings were black. Blanketed in sulphurous soot from coal fires – the famous London “pea souper” fogs – a thin layer of carbon coated every surface in the city. London was so dirty that there was no memory that it might ever have been any other way. During the restoration of 10 Downing Street in 1954, it was discovered that the familiar dark facade was not actually black at all, but originally yellow…