The thermochromic properties of the ceramic colour standards

Thermochromism is a reversible change oftransmittance, reflectance, or absorptance induced by a change of temperature. Photochromism is the corresponding effect induced by optical radiation. These effects can occur in the use of reflectance standards, as they may undergo a considerable temperature rise when subjected to the polychromatic irradiation used by many measuring instruments. An investigation of any thermochromic (and photochromic) properties of the twelve Ceramic Colour Standards is described. It is shown that thermochromic effects are only significant to a very small extent in about half of the standards and not at all in the remainder, while there is no evidence of any photochromism.