Abstract: The invention relates to indicator ink compositions that contain a water-based dispersion of a phenol-formaldehyde resin, at least one colorant and an amine-terminated catalyst. These indicator ink compositions are fixed to a surface, such as by drying, and respond to specific conditions of time, temperature, humidity, pressure and the presence or absence of certain chemicals by changing color. Compositions provide a means for detecting exposure to a predetermined condition and can be fixed or otherwise attached to nearly any article or designed into patterns on materials. Exposure of the indicator ink to the specific condition, the indicator ink provides a permanent detectable record of the event. Further, by varying the amount of amine-terminated catalyst in the formulation, the specific conditions at which the indicator composition will change color can be altered. Such compositions are specifically useful for determining the effectiveness of a sterilization process.