Abstract
In the cultural heritage preservation of medieval buildings, it is common to find plaster walls covered in lime, which previously were painted in polychromy. The conservation interventions usually try to remove the whitewash, whilst maintaining the original color of the painted wall as much as possible. However, there is no agreement on which cleaning technique best preserves the original appearance of the colored plaster. Different pigments found below the lime layer may behave differently depending on the cleaning technique used. Usually, colorimetric or photometric area-based measurements are carried out to study the color of the cleaned areas to compare with their original color, obtained from pre-made plaster probes. However, this methodology fails when the mean color difference is not enough to fully characterize the changes in texture and color appearance. This study presents a set of experiments carried out using two different pigments (cinnabar and malachite) covered with lime, and treated with nine different cleaning techniques on plaster probes prepared according to medieval techniques. We have studied the effect of the cleaning process on the color and the homogeneity of the samples using a hyperspectral imaging workflow. Four different analysis methods are presented and discussed. Our results show that the proposed analysis is able to provide a much more comprehensive and diversified characterization of the quality of the cleaning method compared to the commonly used colorimetric or photometric area-based measurements.
Highlights
One of the main problems that medieval plasterwork presents, as far as its conservation and restoration is concerned, is the risk involved with the cleaning processes used
To make the probes the results from 10 samples analyzed with X-ray diffraction from the plasterwork of the Patio de las Doncellas in the Real Alcázar analyzed with X-ray diffraction from the plasterwork of the Patio de las Doncellas in the Real de Sevilla [16] were taken as a reference
If we look at the sRGB renderization of the samples both before and after the cleaning process, we can see how the more similar color to the original sample is method number 3 (AB57 + scalpel); with this method, some clear patches of white residue have been left after the cleaning, and the high values of inhomogeneity indexes would not be an asset of this method
Summary
One of the main problems that medieval plasterwork presents, as far as its conservation and restoration is concerned, is the risk involved with the cleaning processes used. Layers of various materials were applied one on top of the other to change the original appearance of the plasterwork. They were whitewashed to adapt to the neoclassical taste or for hygiene reasons, or on the other hand, the polychromy was redone to refresh or renovate colors which had been lost over time. An example of this kind of actions from the plasterworks of patio de las Doncellas in Real Alcázar of Sevilla is shown in (Figure 1) [2].
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
