Spectral information to get beyond color in the analysis of water‑soluble varnish degradation
Metadata
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Martínez Domingo, Miguel Ángel; Valero Benito, Eva María; Huertas Roa, Rafael; Durbán, M.; Espejo, T.; Blanc, R.Editorial
Springer Nature
Materia
Yellowness index Spectral reflectance Spectral imaging Cultural Heritage
Date
2019-10-07Referencia bibliográfica
Domingo, M. M., Valero, E., Huertas, R., Durbán, M., Espejo, T., & Blanc, R. (2019). Spectral information to get beyond color in the analysis of water-soluble varnish degradation. Heritage Science, 7(1), 79.
Sponsorship
Spanish Ministry of Economy and Competitiveness, under research Grant DPI2015-64571-R. Spanish State Agency of Research (AEI) and the Ministry for Economy, Industry and Competitiveness (MIMECO) by means of the Grant Number FIS2017-89258-P with European Union FEDER (European Regional Development Funds) support.Abstract
Spectral images were captured of paper samples varnished with two water-soluble materials: gum arabic and egg
white. The samples were submitted to degradation processes that partially or totally eliminated the varnish from
the substrate (water immersion and ageing). 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. 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 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. 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.