Implications of lead isotope variation in lead white from 17th century Dutch paintings

Lead white is a lead (Pb) carbonate that has been extensively used throughout human history. Analysing lead isotope ratios of lead white potentially gives information on the provenance of the lead constituting the pigment. The extensive use of lead white in oil paintings until the 20th century, combined with lead isotope analysis, provides information not only on the provenance of the lead in the pigment but also on painting making processes, trading of lead, lead white throughout history and attribution and authentication. This research presents a comprehensive study of the application of lead isotope analysis to: - Improving analytical precision and sensitivity of lead isotope analysis - Investigating the heterogeneity of lead isotope ratios in lead white used within a single painting - Study of the time-dependant variation of lead isotope ratios of lead white in 17th century Dutch paintings - Use of lead isotope analysis of lead white in combination with other analytical techniques to study paintings The proposed development of improved and more sensitive analytical methods lead to the creation of a new sampling tool, named “micro-scalpel” that allows sampling from cross-sections. This instrument reduces the amount of pictorial material taken during the sampling, and allows the operator to selectively sample from one pictorial layer at a time. Simultaneously the analytical method was improved, increasing the sensitivity of the instrument (multi collector inductively coupled plasma mass spectrometer or MC ICPMS) with the application of a lead double spike (DS) technique and the use of a 1013 Ω resistor amplifiers. Due to the improved analytical sensitivity, the sample size required for analysis was reduced by a factor of ten with the use of 1013 Ω resistor amplifiers, while maintaining accuracy and precision. The new method was used to investigate the heterogeneity of lead isotope ratios within a single painting. The study was conducted on five Netherlandish paintings from the 17th century. Each painting was sampled several times (n. 5-20) in different areas. The data were then compared to the analysis of powdered lead white (historical Venetian lead white from the end of the 16th century rescued from a shipwreck). The study determined that the lead isotope ratios of the Venetian lead white pigment were homogeneous. In contrast, four out of the five paintings contain lead white samples that were outside analytical, identifying lead isotope ratios heterogeneity within the painting. The results suggest that the pigment, processed and used in the artist’s studio prior to painting could have been in contact with other lead-bearing compounds that altered the original isotopic composition. These findings suggest multi-sampling strategy, and the need of a database to compare data to have a reliable interpretation of lead isotope ratios. The lead isotope analysis of 77 dated Dutch paintings from 27 artists allowed assessment of the time-dependent variation of lead isotope ratios of lead white and the creation of a database. The lead isotope compositions recorded a clear time dependence identifying a shift in lead isotope ratios during the period 1642-1647, and a second change is indicated after 1680. The changes in lead isotope ratios in lead white were connected to historical events. For example, the period 1642-47 coincides with the English Civil War in the country that was the main producer of lead at the time. The identification of a time-dependent variation of lead isotope ratios of lead white gives the possibility to distinguish early and late works by individual artists active in the 17th century.