During the development process of a jet engine, it is critical to validate the thermal- and secondary air system. The validation requires an adequate measurement of the temperature distribution on hot end components, as combustor parts, turbine blades and vanes. Rolls-Royce is using irreversible thermochromic paints for measuring the spatial temperature distribution. The paint is a sensitive coating which irreversibly changes its characteristics with temperature and time on condition. For the prior art analysis process, the visual appearance of the paint is assessed and compared to calibration references for temperature prediction. This process requires special trained personnel and a standardised working environment. Previous research investigated the automation of the analysis process using imaging techniques. It is vital to explore these methods to increase the accuracy and precision of the measurement and accelerate the analysis process. However, especially for high temperatures, the change in colour is difficult to distinguish.To supplement the visual analysis process, it is proposed to measure the specular reflectance and roughness of the surface in addition to the colour change. This paper investigates the correlation of these surface characteristics to temperature. Three frequently used paint types for high temperature application have been coated onto Nimonic®75 reference material, which have subsequently been heat-treated in a calibration furnace to generate solid state test pieces. The specular reflectance and roughness of the test pieces was measured with non-intrusive optical measurement devices. For all three paints, a correlation between reflectance and temperature was found. For roughness, the measurement suggests a correlation with temperature in higher ranges between 900 to 1200 °C. For validation, test pieces with a gradual temperature profile have been investigated. To include the effect of curvature, turbine blade test pieces have been measured and evaluated. The results show that measurement of the surface characteristics, like reflectance and roughness, contribute and supplement the analysis process especially in the high temperature range of irreversible thermochromic paints and hence aid the robustness and accuracy of the assessment.