Thermal analysis coupled with the measurement of temperatures at which colour changes are observed in situ was used to test various inorganic pigments with the aim of introducing them into the compositions of thermo-indicating paints. Through a reversible or irreversible modification of the colour these can indicate an undesired increase in temperature of a fluid in a metallic enclosure. Three such pigments are described, which indicate temperatures of 110, 300 and 400°C. The paint contains the thermo-indicator pigment, soluble glass as binder and either ultrafine silica or silica gel, or a mixture of Na2SiF6 and finely-ground sand as hardener. Such paints are used for damage warning.