Interdependence between color and gloss is a concept well-known by artists, especially by old masters, but is not usually considered in material characterization. Indeed, measurement methods and definitions consider these two attributes individually. This research investigates how the available measurement methods for gloss and color (saturation) fit with corresponding perceptual qualities, glossiness and saturation. The definitions of both measured quantities, as well the measurement methodologies, were developed for reference materials (ceramic tiles for color and dark glass specimen for gloss) not representative of artwork materials and do not consider observation conditions similar with those adopted during exhibitions. The prediction of material appearance is recognized as one of the most important challenges in applied metrology, because appearance is the key to achieve effective exhibitions and consumers choices. The results of this study highlight that the two perceived qualities are mutually related, as well the measured quantities: gloss and saturation mutually interfere and the measurement methods and quantities are not uniform with the perceived qualities and the colorimetric coordinate C* no longer describes the perceived saturation.
The paper presents an investigation on the correlation between spectral characteristics and conservation conditions of parchment to define a NON invasive methodology able to detect and monitor deterioration process in historical parchment without the need of taking small samples. To verify the feasibility and define the most appropriate measurement method, several samples of contemporary parchments, produced following ancient recipes and coming from different animal species, with different degrees of artificially induced damage, were analyzed. The SRF and STF of each sample were measured in the same point, before and after each step of the artificial ageing treatment. Having at disposal a parchment coming from a whole lamb leather, allowed also the study of the correlations between the variations of SRF – STF and the intrinsic factors of a parchment like the variability of animal skin anatomy and of manufacturing. Analyzing different samples allowed also the definition of the measuring method sensitivity and of reference spectrum for the different animal species parchments with accuracy limits. The definition of a reference spectrum of not damaged parchment with acceptability limits is a necessary step for understanding, through SRF – STF measurements, historical parchments conservation conditions: indeed it is necessary to know if deviations from the reference spectrum are ascribable to damage or only to parchment anatomic/production variability. As a case study, the method has been applied to two historical parchment scrolls stored at the Archivio di Stato di Torino (Italy). The SRF - STF of both scrolls was acquired in several points of the scroll, the average spectrum of each scroll was compared with the reference spectra with the relative tolerance limits, recognizing the animal species and damage alterations and demonstrating the feasibility of the method.
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.