Fundamental Studies on the Aqueous Cleaning of Contemporary Acrylic Emulsion Paintings.

摘要

The chemical, physical and visual responses of seven Golden Artist Colors heavy-body pigments aqueous cleaning solutions were measured to elucidate aqueous cleaning conditions that minimize film swelling, extraction of octylphenol ethoxylate (OPEO) non-ionic surfactant and mimimize color changes. 192 cleaning solutions were tested that varied in pH, conductivity and ionic species (NaCl, Na2SO4, CaCl2). After cleaning, OPEOs were identified in the cleaning solution extracts and quantified using tandem mass spectrometry. Results indicate that high conductivity, low pH cleaning solutions minimize OPEO extraction and film swelling. While low pH solutions tend to minimize swelling, they are of little practical use for developing aqueous cleaning systems due to notable film color changes. Solution conductivity, above or below the film isotonic point (6--10 mS cm-1), was found to be more influential than pH in determining optimum cleaning conditions to minimize chemical, physical, and visual changes in the cleaned films. The nature of the ionic species present in the cleaning solution to tailor the conductivity was rationalized using the Hofmeister Series. This provided insight into the salting-in and salting-out effect of the ions in the aqueous cleaning solutions and was further validated through solution cloud point temperature measurements. Taken as a whole, Na2SO4 solutions near pH 7.5 and at conductivities greater than 6 mS cm-1 are effective at both reducing swelling and minimizing the extraction of surfactant from the test paint film. In terms of the practical cleaning and preservation of acrylic paintings, the implications are clear; managing the conductivity and the predominant ionic species in a cleaning solution can help to reduce the extraction of surfactant from the painting surface, maintain the mechanical integrity of the paint, and preserve the artist's original intent.