How to efficiently characterize special effect coatings.

Coatings and plastics that contain special effect pigments show angular-dependent reflection characteristics. Interference pigments, for instance, exhibit a color impression ("appearance") that changes with the directions of illumination and observation. It is currently an open question how the appearance of such coatings can be best characterized without extensive measurements of the spectral radiance factor. In this paper, a simple and efficient approach is presented on how to characterize the appearance of surfaces composed of metallic and interference pigments. Based on the rotational symmetry of the pigment distribution around the surface normal, it is demonstrated how the appearance at any configuration of illumination and observation can be estimated from a set of in-plane measurements. For practical applications, it is shown that a rather small number of geometries (e.g., 10) are sufficient. The presented methodology is an alternative to a recent principal components analysis-based procedure and offers the advantage of being based directly on an extensible physical model while having at least the same prediction accuracy.

Comparison measurements of 0:45 radiance factor and goniometrically determined diffuse reflectance.

A comparison between the absolute gonioreflectometric scales at the Helsinki University of Technology (TKK) and the Physikalisch-Technische Bundesanstalt (PTB) has been accomplished. Six different reflection standards were measured for their 0:45 spectral radiance factor between 250 and 1650 nm in 10 nm intervals. Also, the 0:d reflectance factor between 400 and 1600 nm in 100 nm intervals was determined from goniometric reflectance measurements over polar angles with subsequent integration within the hemisphere above the sample. Goniometric comparisons covering such an extensive wavelength range and also several different sample materials are rarely implemented. For all but one sample, the difference between the results obtained at the TKK and the PTB was, with the exception of a couple of measurement points, within the expanded uncertainty (k = 2) of the comparison at least up to a wavelength of 1400 nm. All differences between the measurement results can be understood, except for one translucent sample in the visible wavelength range. The effect of sample translucency was found to be significant in the NIR wavelength region. Also, a general tendency of an increase of the TKK values relative to the PTB values in the UV region was observed. Possible causes for this phenomenon are discussed.