This type of paints display changes and/or history in temperature in colors, attracting attention in sanitary management of food, etc.
Thermoindicator paints use pigments that clearly show color changes at specific temperature, and there are following types.

(1) Irreversible thermoindicator paint

This type utilizes irreversible color changes by temperature changes, and contains cobalt, nickel, iron, copper, chromium, and manganese salts as the pigments containing amine, ammonium, carbonate groups, and oxalic acid in the composition.
Color changes occur by changes of the compounds themselves with thermal decomposition generating ammonia, carbon dioxide gas, and water, and the color changes are irreversible.
Once the color changes occur, the colors will not reverse back to the original color, even when the temperature is reduced. Applicable range: 50〜400℃.

(2) Reversible thermoindicator paint

The pigments used for this type of thermoindicator paints utilize color changes associated with crystalline form transition, and are used on Ag2HgI4（color change temp. 50℃）, Cu2HgI4（70℃）、Ag2HgI4-Cu2HgI4 Solid solution (35〜70℃), and organic dye compounds.
These paints change color when thermoindicating temperatures are reached, and return back to the original colors when the temperatures decrease.

(3) Cumulative thermoindicator paint

This type of thermoindicator paint is though irreversible, color changes occur with synergistic effect of temperature and time. Sulfur compounds and a mixture of polyvalent metal compound added to this are used as thermoindicating material. The color changes occur when heated for certain lengths of time under the existence of water vapor, generating a sulfide of the polyvalent metal.

(4) Semi-reversible thermoindicator paint

This paint uses thermoindicating compound that changes color by losing crystallization water when heated, but returns to the original color by taking in crystallization water again in highly humid atmosphere. Hexamethylenetetramine salt of Ni or Co are commonly used.