Lithographic stamps printed in two or more colours are printed from two or more stones. The first stone bears the key design, or outline pattern, repeated to the required number of units. A specially prepared proof from this, on a non-stretching paper, is the key-sheet; on this transfers are laid in correct position for the first colour; the transfers adhere to the stone, leaving the key-sheet free to receive the transfers for the next colour. And so stone after stone is laid down, each in correct register with the rest, to do its part in the colour scheme. The key-stone is not necessarily used in the actual printing.