Investigation of smalt in cross-sections of 17th century paintings using elemental mapping by laser ablation ICP-MS

Abstract

Microanalysis by laser ablation-ICP-MS was performed on 17th century paint cross-sections of two Dutch masters (Hendrick Avercamp and Caesar Boetius van Everdingen) and a Chinese coromandel lacquer (unknown artist) to study the multi-elemental composition of the blue pigment smalt. Smalt is a potassium silicate glass colored by cobalt ions which are often associated with other elements such as As, Ni, Bi and Fe. Due to interactions between pigment and medium, smalt often deteriorates as a result of potassium leaching, thus losing its color and causing chemical and physical changes in the paint film.Elemental mapping by laser ablation-ICP-MS was carried out for a suite of 54 elements using line scanning (20–50 parallel laser tracks). Elemental maps with pixel dimensions of 5μm were generated for sample areas containing all the layers of the cross-sections. Elemental quantification of the smalt particles was carried out by a sum normalization calibration protocol based on summation of the elements as their oxides to 100wt.% and using relevant glass standards. Elemental concentrations in the maps of 5–30μm sized smalt particles were visualized in pseudo-colors.Next to highlighting the microanalytical potential of laser ablation-ICP-MS for multi-elemental mapping (on trace, minor and major element levels simultaneously) of smalt in paint cross-sections, this work will elaborate (statistical) data processing protocols for elucidation of cobalt ore provenance, possible deterioration mechanisms and the conservation state of the three examined paintings.