Stability of acrylic and alkyd paints during the laser cleaning of painted surfaces

Suzana DAN, Joakim STRIBER, Roxana RADVAN, Roxana SAVASTRU, Mihai POPESCU, Camelia COMSIA

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As a large number of studies have reported, one of the most important problems in the restoration of polychrome surfaces with laser-cleaning techniques is colour alteration. A comprehensive examination of the object to be cleaned is required. It should include a well-researched history of the object and a serious analysis of the original materials, as well as those used during past restorations (repainting, chromatic integration, etc.). The chemical compositions of the pigments from different periods and from different schools of restoration are varied and have individual responses to the laser irradiation. New materials used in painting embrace a large territory, especially in large outdoor paintings. Their behaviour in laser-cleaning treatment must be known in advance for various applications - painting cleaning, chromatic integration, graffiti cleaning, etc.

This work has been based on the chromatic analysis (CIE Lab, reflectance measurement), and X-ray diffraction analysis of various irradiated samples of modern materials, such as acrylic and alkyd paints and different varnishes. Our attention has been focused on modern material stability after controlled laser irradiation. The most popular medium and the first to challenge the supremacy of oils has been acrylic resin emulsion, since this polymer combines most of the expressive capabilities and density of oils with the quick-drying properties and transparent brilliance of tempera and gouache. It is made by mixing pigments with synthetic resin and thinning with water. It shows little colour change in drying, and does not darken with time. Acrylic colours are considered to be less affected by heat and other destructive forces than oil paint. Because of all these desirable characteristics, acrylic paints became immediately popular with artists whenthey were first commercially promoted in the 1960's.

Suzana Dan, Joakim Striber, Roxana Radvan, Roxana Savastru
National Institute of Research and Development for Optoelectronics
Centre for Restoration by Optoelectronical Techniques (CERTO)
1 Atomistilor St., Bucharest-Magurele, Romania
e-mail: radvan@inoe.inoe.ro

Mihai Popescu
National Institute of Materials Physics
Platform Magurele
76900 Bucharest, Romania

Camelia Comsia
National Art Museum of Bucharest
Calea Victoriei 49-53
70101 Bucharest, Romania