Goniochromatic difference between effect coatings: Is the whole more than the sum of its parts?

Special effect coatings have been increasingly used in many industries (e.g. automotive, plastics industry) over the past two decades. The measurement of perceived color differences on such coatings cannot be done by means of traditional color-difference formulas (e.g. CMC(l:c), CIEDE2000, AUDI2000) as they lack to consider distinct optical properties such as coarseness, glint and goniochromatism. However, there is a need to ensure quality and colorimetric accuracy when designing and processing special effect coatings. In this paper, we present a psychophysical experiment intended to serve as a basis for future work on a new generation of color-difference formula(s) for multiple viewing geometries (viewing and illumination angle). We are especially interested in assessing whether judging under a single geometry can lead to different results as judging under several (two) geometries, i.e. whether the sum is more than its part.