These well-known figures are generally produced by placing a coin on one side of a piece of glass, and on the other side opposite it another coin or small plate of metal. The coin and the plate are then strongly electrified—the one positively, the other negatively. When the coin is afterwards removed, and the surface of the glass on which it rested is breathed on, there is developed an image of the coin, showing many of the details of the engraving. The image is produced by the condensed moisture being deposited in different-sized patches at different places.