When people list history’s most world-changing inventions, they usually include fire, or guns, or computers. Rarely do people mention something so ubiquitous to us that it has become, literally, invisible – glass and transparent plastic. In the Renaissance, though, when glass began to be sheeted and shaped in quantity and with skill, it created a boom in civilisation; microscopes and telescopes opened up the breadth of the world to science, spectacles doubled men’s intellectual lifetime, and windows allowed for the creation of the first greenhouses.