As part of the research activities for the MANUNET Lasclean 2008 Project (MANUNET transnational call 2008) laser cleaning technology tests were conducted on metallic samples and artefacts of artistic interest.
In collaboration with the Fonderia Artistica De Carli, seven series of metal alloy samples were made, of the type used to produce both ancient and contemporary works of art: a historic bronze alloy (Cu 88: Sn 12) and a modern aluminium alloy (SGAlSi91) with different surface finishes (mirror polished, sanded, black liver of sulphur finish and green patina for the bronzes and mirror polished, sanded and black patina for the aluminium). The samples were treated with the protective coatings widely used in the art conservation sector - a micro-crystalline wax (Reswax) and an acrylic resin (Incral 44) - and subsequently aged naturally by direct exposure to the elements of an aggressive urban environment.
Three different types of laser instrumentation were used, an LQS (EOS 1000 LQS made by the company El.En. SpA), an SFR (EOS 1000 SFR made by El.En. SpA) and a QS (RAFFAELLO, made by Quanta System SpA) and applying two different operating procedures: cleaning in controlled, reproducible firing conditions, and cleaning entrusted to the sensitivity of the restorer.
The research project had a series of aims:
to assess the efficiency of the technology in removing the aged protective layers;
study the morphological and chemical changes in the cleaned substrata;
study the effects of laser radiation on artificial coatings;
determine the damage and ablation thresholds of the materials;
study the varying subjective assessments made by the highly qualified operators involved.
The optimal fluence parameters determined by the tests on the metal samples were subsequently tested on the more complex surfaces of two statues in bronze and aluminium.