5/2/2023 0 Comments Medieval manuscripts art![]() ![]() This work collects the results obtained from the colorimetric study carried out on a series of samples of paper with varnish exposing to different physical-chemical tests (humidity, immersion in water, dry heat and accelerated aging) tests that recreate adverse conditions to which this type of woks may be exposed as a consequence of its natural aging, the action of certain degradation factors or the restorative action. ![]() Knowing the chromatic variations of these materials is essential for their selection as a conservation varnish. Over time, or due to adverse conditions, these varnishes undergo a series of degradations in their color that can distort the original appearance of the underlying work. The use of varnishes as a final coat in graphic work fulfills an aesthetic and protective function. To sum up, the main contributions of this study are the characterization of the spatial homogeneity through pixel-based spectral and color information and the proposal of spectral-based yellowing indices for two critical applications (ageing process follow-up and effect of cleaning), as demonstrated with synthetic and historical samples of varnished paper respectively. The potential uses of spectral information are demonstrated with several pieces of a real antique map sample by comparing the spectral information measured before and after cleaning the sample. Since the varnishes typically become yellower with ageing, this study introduces two novel and simple-to-compute yellowness indices based on the spectral information, which are validated against a standard colorimetric index (ASTM-E313 2015). ![]() The spectral information was used to obtain average color data and to characterize the spatial and color inhomogeneity across pixels, showing that the pixel spectral data are critical for an accurate characterization of the degradation process of the varnishes. The samples were submitted to degradation processes that partially or totally eliminated the varnish from the substrate (water immersion and ageing). Abstract Spectral images were captured of paper samples varnished with two water-soluble materials: gum arabic and egg white. ![]()
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