Measuring the colour of reflective surfaces
The colour of a material or object can be represented by its spectral 'fingerprint' (its spectral reflectance or transmittance) or in terms of colorimetric values such as (but not limited to) x, y, u', v', L*, a*, b*. These can be calculated for CIE 2° and 10° Standard Observers and CIE Standard Illuminants A, C, D50, D65.
At NPL we measure the colour of reflective samples using a calibrated spectrophotometer which may be used in 0°:45°a, specular included (8°:di) and specular excluded (8°:de) geometries and has a resolution down to 1 nm over the spectral range 380 nm to 780 nm. The results are traceable to the NPL spectral reflectance scale and are UKAS accredited. Services for colour of transmissive materials are also available.
We can measure customer samples or can supply a range of specially-developed transfer standards, including the widely-used CCS II ceramic colour standards. The latter consists of 12 coloured ceramic tiles, designed specifically both for calibration purposes and to test various aspects of the performance of colour-measuring instrumentation such as linearity, stray light and colour discrimination. Various other ceramic reflectance standards are also available, including black, white, metameric pairs (which look similar under daylight but different under other light sources) and a holmium-doped tile (for wavelength calibration). All the tiles are available with a glossy or matt finish.