Warty nodules on the edges of electrotypes are usually caused by the employment of small currents. This may happen by using a small cell or small elements in the cell, or by the employment of connecting wires having a high resistance. It is unusual to find these nodules on edges protected with paraffin, and their existence points to a soiling of the parts whilst blackleading the mould. When these nodules are troublesome, it is usual to take out the moulds, cut or file off the warts, give the copper a dip in nitric acid to clean it, then re-immerse the electrotype, and proceed with the deposition.