a paint containing various chemical compounds that are capable of changing color at a certain temperature. The change may occur, for example, as a result of breakdown of a heat-sensitive compound, such as ferric hydroxide or cadmium carbonate, or the formation of a new compound as a consequence of the reaction of the temperature-indicating components of the paint—for example, the formation of lead sulfide from thiourea and lead tetroxide. A distinction is made between reversible paints, which can repeatedly return to their original color, and irreversible paints.
Temperature-indicating paints, which are produced in the form of pastes or sticks, can be used to measure temperatures in the range from 35° to 1600°C, with an accuracy of ±0.5° to ±10°C. They are used in cases in which the use of the usual means of thermometry is difficult or impossible.