Copper Carbonate: Blue Vitriol Precipitated with Washing Soda

Pour washing soda into a solution of copper sulfate and a pale blue sludge falls out; warm it and it turns into a dense green powder. George Fownes (1856) gives this as the way the pigment is made; it is close in make-up to the mineral malachite. Potters and glassmakers use it as a copper colour. The picture: a heap of basic copper carbonate powder.