Colorimetry to assess the visual impact of dust deposition on mosaics at sheltered archaeological sites

Abstract

One of the most important alteration factors for archaeological sites is the deposition of dust, primarily onto horizontal surfaces, because it affects both the conservation state of the remains and their appearance. The deposition is responsible for visual changes that prevent proper appreciation of the site, and this is especially negative for the decorative elements such as mosaics. Dust deposition has been seen as a significant problem in sheltered sites as opposed to those located in the open air, where deposits are regularly washed away. However, there is a lack of knowledge on the visual effects of dust on sheltered archaeological remains despite the fact that this information could help to determine cleaning regimes. This research has been undertaken at the House of Hippolytus, a Roman villa located on the outskirts of Complutum, situated where the city of Alcalá de Henares (Spain) stands today. The site was covered with a partially enclosed shelter in 1999 and it contains a magnificent mosaic in the central area. This ornamental floor is the center of attention for visitors and has often been used as a promotional image because of its high artistic value. This study has objectively evaluated the visual changes (color and spectral characteristics) of the mosaic at the House of Hippolytus before and after being cleaned with dry and wet systems using a novel approach based not only on a spectrophotometer (CM-2600d Konica Minolta®) but also on a LumiCam® 1300 camera (Instrument Systems GmbH). Although wet cleaning implies the use of water, which is a decay factor, it has been found to be the best option for recovering the original aspect of the mosaic.