Modeling of the color decay and calculation of the original state: the case of San Telmo (18th century), Seville, Spain

The mural painting Glorification of the Virgin at Palace of San Telmo (18th century, Seville, Spain) has been analyzed through 161 optical spectra acquired using fiber optic VIS-NIR reflectance spectroscopy, encompassing all the colors present in the painting. In addition, 13 samples were taken from representative areas and analyzed by optical and electronic imaging. These analyses have identified the painting materials and techniques and provide information about the color generation processes through the interaction between different pictorial layers. The color alterations suffered by the painting have been quantified through a mathematical model which yields the original color and attributes. The results find a general darkening and color shift more noticeable for cold colors, showing that the mathematical model is a reliable approach to color correction and supports the use of fiber optic VIS-NIR reflectance as a non-invasive technique for the characterization of cultural heritage. • Alteration of colors at the mural painting Glorification of the Virgen del Buen Aire chapel at San Telmo Palace is measured and modeled. • Reflectance VIS-NIS spectra (161) samples all the colors at the mural painting. A mathematical model that quantifies color alteration is proposed. • The results find a general darkening and color shift, showing that the mathematical model is a reliable approach to color correction and supports the use of fiber optic VIS-NIR reflectance as a non-invasive technique for the characterization of cultural heritage.