Goniometric and colorimetric properties of paints and varnish

The spectral reflectance of different samples of three different hues, (red, green, blue) with four different protective varnishes was measured in 8/d condition and with a goniometer equipped with a spectrometer. The samples are representative of hue and varnishes typically used in works of arts, the characterization was performed to test how the different gloss finishing induced by transparent varnishes affect the spatial distribution of the luminance coefficient in typical lighting arrangements for exposition of works of art. Nowadays the most used transparent protective varnishes are matt or glossy, natural or synthetic. The choice within them is usually made looking at mechanical, chemical (also in term of removal) and protective properties. Varnishes optical properties investigation on saturation and gloss alteration of the perceived artifacts are not usually investigated. Expected results of this research include: analysis of influences on color appearance of protective varnish according to the condition of illumination and observation, suggestion of new additional criteria for varnish selection and lighting set up exposition and reliability of 8/d measurements condition, that is a typical measurement set-up of portable instruments. Our results showed that natural varnishes are more able to change the gloss of the surfaces than synthetic ones, because the shape and intensity of the specular peak for glossy and matt natural varnish are very different. Both synthetic and natural varnishes have different behaviors at 30° or 60° light incidences: at 30° of incidence all samples have smaller variations, while at 60° of incidence the variations are larger, and for some samples the achromatic point is reached.