Color degradation mapping of rock art paintings using microfading spectrometry

Abstract

Rock art documentation is a complex task that should be carried out in a complete, rigorous and exhaustive way, in order to take particular actions that allow stakeholders to preserve the archaeological sites under constant deterioration. The pigments used in prehistoric paintings present high light sensitivity and rigorous scientific color degradation mapping is not usually undertaken in overall archaeological sites. Microfading spectrometry is a suitable technique for determining the light-stability of pigments found in rock art paintings in a non-destructive way. Spectral data can be transformed into colorimetric information following the recommendations published by the Commission Internationale de l’Eclairage (CIE). The fading degree can be evaluated through the color changes produced, computing both color and chromatic differences. Microfading Tester (MFT) measurements on spot samples are time-consuming and difficult to materialize on-site. This paper presents the results of statistical Gaussian process interpolation to map the potential MFT spectral variations overtime on a scene full of prehistoric rock art paintings. In addition, a descriptive analysis of color variations that may suffer the rock art motifs over time has been carried out. The advanced statistical methodology implemented can highlight potential changes on some rock support areas, and stable conditions on the painted red motifs over time, which can help to establish future conservation actions in the archaeological site.