Kid leather or chamois puffer with boxwood knob, containing an orange powder (a mixture of sulfur and red lead). The experiment, invented in 1777 by Georg Christoph Lichtenberg, demonstrates visually the opposite electrical charges of the two coatings of the Leyden jar. First, the brass knob of a charged Leyden jar was drawn over a cake of resin of an electrophorus, and then the operation was repeated on the outer coating, producing a pattern of positive and negative charge on the cake. This pattern then became visible by dusting the cake with the fine orange powder, which became electrically charged through friction as it was expelled from the nozzle. The sulfur settled on to the positive charge, the red lead on the negative charge. This curious experiment illustrates the basic principle of modern photocopiers, in which the toner powder is deposited on electrically charged images.