Nacre is the smooth, shiny layer on the inside of some sea shells. People also call it mother-of-pearl. It has a soft glow — white, pink, silver, sometimes a hint of green — that seems to move when the light moves. Makers slice it thin and set it into buttons, jewellery, and little boxes. A pearl is made of the same stuff: the oyster lays nacre around a tiny grain, layer by layer. The word itself sounds rather special and a bit scientific. In a shop or in everyday talk, most people just say mother-of-pearl; nacre turns up in science, in craft writing, and in careful descriptions of shells.