The earliest reference to a continuous inkjet ink (CIJ) in the 1971 patent US3596285A states " The preferred ink is characterized by viscosity and surface tension characteristics such that the liquid will be maintained over span under the force with which it is moving in bridge or stream. Implicit in such requirement is that the pressure applied to the ink in formation of said stream is sufficient to form a jet and to impart enough energy to carry the jet as a continuous liquid mass notwithstanding the defective forces which are or may be applied. Furthermore, the color of the ink and the color of the carrier should be such that good optical contrast is formed there between the following printing. The preferred ink is a "hot-melt ink". That is to say it will assume a solid phase at the temperature of the carrier and liquid phase at some higher temperature. The range of commercially available ink compositions which could meet the requirement of the invention are not know at the present time. However, satisfactory printing according to the invention has been achieved with a conductive metal alloy as ink. It is extremely hard at room temperature and adheres well to the surface of the carrier.