Colour Change Caused by Dry Cleaning Process on Painted Surfaces

Over the last few years, the dry cleaning process has become an excellent alternative to solvent or water-based mixtures, which prevents diffusing the dirt into the painting structure during the cleaning process. The use of this kind of cleaning is especially effective on contemporary paintings as it prevents the solubilisation of additives such as the surfactants contained in polymeric dispersions (e.g. in acrylic and PVAc-based paints). In addition to some reported side effects that could be caused by dry cleaning processes on paintings (such as changes in the integrity of the paint or any residual materials which may be left behind) one parameter that should be tested is the colorimetric change seen on treated surfaces. In some cases, the use of certain dry cleaning materials can cause burnishing or roughening of the painted surface. This effect results in a change in brightness and chroma and subsequently to a change in the colour of the treated area, especially on dark shades. This article evaluates the colorimetric change of different kinds of painted surfaces caused by the dry cleaning process, such as gouache, commercial formulated acrylic, fish glue tempera, casein tempera, PVAc and primal acrylic paint. The cleaning materials tested include different kinds of sponge cloths, malleable materials and erasers used in the field of heritage conservation/restoration. The change in colour is measured by means of a spectrophotometer and the chromatic values are processed in a spreadsheet. The colorimetric changes have been calculated using the advanced equation recommended by CIEDE2000 and the chromatic values obtained have been studied following the standard recommendations.