Testing the harmfulness of chemical cleaning methods for the removal of incrustations from a glazed stoneware public artwork

Abstract

• Cleaning methods were evaluated for removing a Ca-rich incrustration formed over a crystalline glaze of an stoneware outdoor public artwork that comprised a water jet system. • Incrustration was characterized and cleaning methods were selected: mechanical method (dry microblasting with sand, alumina and peach pit) and chemical methods (HNO 3 , Na 3 EDTA, Ionex H and Kalkrent® an “environmental friendly” commercial detergent). • Harmfullness was tested in laboratory on replicas produced with artist using a multianalytical approach to evaluate the effect of the cleaning methods. • Mechanical methods were damaging, but could be used to reduce the thickness of incrustration. • All chemical cleaning methods caused alteration of the glaze, except Ionex H, altering mostly the glassy phase. Incrustations are a common conservation problem, particularly in artworks exposed to water. Calcium-rich layers tend to build over their surface making cleaning interventions necessary to improve the chemical stability and restore readability. Harmfulness tests are crucial for selecting cleaning methodologies for glazed surfaces due to their mechanical and chemical susceptibility. This study selected a combination of cleaning methods to test their adequacy to remove a Ca incrustations from a modern glazed artwork. The tested methods were mechanical (dry-blasting with sand, alumina and peach) and chemical (HNO 3 , Na 3 EDTA, Ionex H and Kalkrent® an “environmental friendly” commercial detergent). To assess the effect of the cleaning methods replica substrates of the glazed ceramic were subjected to the different methodologies. Harmfulness was assessed by: (i) mass variation measurements to evaluate the material loss; (ii) microscopy techniques (optical, scanning electron and confocal laser microscopy) to evaluate morphological and surface topography alterations and (iii) μ-Raman to detect changes in the glass structure. Results indicated that the glassy phase was the most affected, and Ionex H was the less harmful of the tested cleaning products. The first in situ testing revealed that a combined approach will be most effective using microblasting for reducing the thickness of the incrustation, followed by the selected chemical method Ionex H.