Asked by: Andy Scott, Redcar
Eggshell is primarily composed of calcium carbonate, which is naturally white. Some birds coat the outside of their eggs with a pigment to improve camouflage or help identify their eggs from those of others. The brown colour that coats a hen's egg comes from a pigment called protoporphyrin, which is derived from the breakdown of haemoglobin. Whether a hen lays brown eggs or white depends on its breed. There is a widespread, though mistaken, view that brown eggs are healthier, and so most commercial laying strains have been bred to lay brown eggs. The Maran hen (whose name comes from the French for 'chestnut'), lays eggs that are a deep mahogany colour, but the pigment washes off so easily that when the breed was first introduced to the UK in the 1930s, many people believed the eggs had been artificially dyed.
Luis trained as a zoologist, but now works as a science and technology educator. In his spare time he builds 3D-printed robots, in the hope that he will be spared when the revolution inevitably comes.