Color characterization of coatings with diffraction pigments

Abstract

Coatings with diffraction pigments present high iridescence, which needs to be characterized to describe their appearance. The spectral Bidirectional Reflectance Distribution Function (BRDF) of six coatings with SpectraFlair diffraction pigments were measured using the robot-arm-based goniospectrophotometerer GEFE, designed and developed at CSIC. Principal Components Analysis (PCA) has been applied to study the coatings' BRDF data. From data evaluation and based in theoretical considerations, we propose a relevant geometric factor to study the spectral reflectance and color gamut variation of coatings with diffraction pigments. At fixed values of this geometrical variable, the spectral BRDF component due to diffraction is almost constant. Commercially-available portable goniospectrophotometers, extensively used in several industries (automotive and others), have to be provided with more aspecular measurement angles to characterize goniochromatic coatings based on diffraction pigments.

Evaluation of circulating cell‑free DNA as a molecular monitoring tool in patients with metastatic cancer

“…A total of 15 patients with three common tumor subtypes were assessed. The majority of patients had metastatic disease at diagnosis and the median OS observed in the respective cancer subtypes was in line with previously published cohorts (42)(43)(44)(45)(46).…”

Review of instrumental inter‐agreement study of spectral and colorimetric data of commercial multiangle spectrophotometers

“…However, from a point of view of optical measurement of materials, this is an approximation well understood in the color industry using goniochromatic materials because the main source of optical and spectral data is the bidirectional reflectance distribution function (BRDF) concept . For goniochromatic materials, from metallic to interference and diffractive effects, the main challenge for color instrumentation manufacturers is to measure correctly with the minimal number of geometries to obtain the maximum spectral and colorimetric information, that is, predicting accurately the complete BRDF, and the corresponding color palette of any goniochromatic material . However, this is not trivial because it means one must take into account the structural information (flake orientation, measurement geometry into the flake particle, etc.)…”

Angular and Spectral Bandwidth Considerations in BRDF Measurements of Interference- and Diffraction-Based Coatings

“…The spectral BRDF of goniochromatic surfaces changes in great extent for different combinations of illumination and viewing directions (geometries), and it makes their colorimetric description complex. Most of the research work on the appearance of goniochromatic surfaces has dealt with the proper methodology to describe their color by selecting adequate geometries, and to use measurements for representing such surfaces [6][7][8][9][10][11][12][13][14][15][16][17]. However , the metrological aspect of measuring the spectral BRDF and the color with real instruments, which have finite-size apertures, has not been systematically studied yet as in this work.…”

“…Since the deflection depends on the wavelength, the color at a given observation direction depends on the deflection angle with respect to the normal direction to the pigment. In coatings based on diffraction pigments, the color shift reveals very clearly when varying the aspecular angle at a constant incidence angle [2,[15][16][17]31]. An example of this color shift with the geometry is shown as a CIE a*b* diagram in Figure 2, for one of the highly goniochromatic diffraction-based special effect coating studied in Reference [15] (SpectraFlair R Silver 1500-14).…”

“…In coatings based on diffraction pigments, the color shift reveals very clearly when varying the aspecular angle at a constant incidence angle [2,[15][16][17]31]. An example of this color shift with the geometry is shown as a CIE a*b* diagram in Figure 2, for one of the highly goniochromatic diffraction-based special effect coating studied in Reference [15] (SpectraFlair R Silver 1500-14). Again, solid lines represent those geometries with constant aspecular angles and different incidence angles, and it can be noticed that the hue variation is much smaller at constant aspecular angle than at constant incidence angle and varying aspecular angles, when it is possible to obtain all hues with roughly the same chroma for a given incidence angle.…”