Abstract: An ink composition is provided which is suitable for use on plastic, bare metal, for example, tinplate or aluminum as well as on such metals having organic coatings applied to surfaces thereof. The inks are suitable for use in contact printers or in jet ink printing techniques and apparatus. The ink compositions are thermotropic, i.e. they change color in the presence of water or steam at elevated temperature and are useful as sterilization or pasteurization indicators. The inks comprise essentially a binder resin component, or mixture of such resin components, an alcohol solvent and a combination of dyes which produce a visible and permanent color change in the presence of water or steam at elevated temperatures.