NOVELTY - Method of determining a thermal history of a component (I), which is subjected to an operative, thermal environment, in particular a high-temperature environment, comprises: (a) providing a detection material (II) to (I) (where (II) comprises an amorphous host and doped with at least one luminescent dopant); (b) exposing (I) to the operative, thermal environment; (c) measuring at least one luminescence characteristic of (II); and (d) determining the thermal history of (I) from the measured at least one luminescence characteristic of (II).    USE - The method and the system are useful for determining thermal history of components that are subjected to high-temperature environments such as in boilers, fuel cells, furnaces, engines, gas turbines, turbine blades, boiler liners or parts of internal combustion engine.    ADVANTAGE - The method provides an optical readout process, which is both fast and easy to perform and consequently enables inter alia a faster design process. The paint does not require the use of toxic metals such as lead and chromium or the use of noble metals such as silver or gold, thus cost effective. The method provides luminescent material composition that are operative in higher-temperature environments, typically from room temperature to 1300 degrees C and above, and can be used to indicate a thermal history or past temperature exposure. The luminescent material compositions allow the indication of thermal history at ambient temperature. The luminescence of the luminescent material can be easily measured with an instrument such as a camera, a horoscope or a photomultiplier device, which enables the operator to read out the thermal history of the luminescent material when the data is compared with pre-calibrated data.    DETAILED DESCRIPTION - Method of determining a thermal history of a component (I), which is subjected to an operative, thermal environment, in particular a high-temperature environment, comprises: (a) providing a detection material (II) to (I) (where (II) comprises an amorphous host, which is in an amorphous/glassy state prior to exposure to the operative, thermal environment and doped with at least one luminescent dopant); (b) exposing (I) to the operative, thermal environment; (c) measuring at least one luminescence characteristic of (II) following exposure of (I) to the operative environment (where the luminescence characteristic is a function of the crystallization of the amorphous host of (II) and the exposure of (I) to the operative environment); and (d) determining the thermal history of (I) from the measured at least one luminescence characteristic of (II). INDEPENDENT CLAIMS are included for:    (1) a system, for determining the thermal history of the component (103) to which is provided (II) and which is in use subjected to the operative, thermal environment, comprising: (i) a detector (111) for measuring at least one luminescence characteristic of (II) following exposure of (I) to the operative environment; and (ii) a processor for determining the thermal history of (I) from the measured luminescence characteristic of (II);    (2) the detection material (II) for use in determining the thermal history of (I);    (3) a coating (105), applied to (I), comprising (II); and    (4) a paint, for application to (I), comprising (II); and    (5) the component (I) comprising (II) within its body.    DESCRIPTION OF DRAWING(S) - The diagram shows a system for determining the thermal history of the component, which is subjected to a high-temperature environment.    Monitoring system (101)    Component (103)    Coating (105)    Detector (111)    Input means for an operator to input information in operating the monitoring system. (115)