Old Masters’ lead white pigments: investigations of paintings from the 16th to the 17th century using high precision lead isotope abundance ratios G. Fortunato, a A. Ritter a and D. Fabian b Received 16th December 2004, Accepted 8th March 2005 First published as an Advance Article on the web 15th April 2005 DOI: 10.1039/b418105k White lead (2PbCO 3 ?Pb(OH) 2 ), a common component in 17c. artists’ painting materials, was singled out to investigate the potential of lead isotope abundance ratios in the field of authentication and origin assignment. Paintings by Peter Paul Rubens, Anthony van Dyck and other Old Masters of the Northern and Southern schools were chosen for this study. An interdisciplinary approach was chosen using both analytical instrumental methods, art technological and art historical knowledge. Minute samples taken from paintings from selected art collections worldwide were investigated using mass spectrometry, scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX). The high precision lead isotope abundance ratios were measured by multiple collector inductively coupled plasma mass spectrometry (MC-ICP-MS). The determination of the calcium matrix influence with respect to possible bias effects to the isotope ratios gave clear decision support, to whether a result lies within the stated combined measurement uncertainty of the result, to eliminate time-consuming matrix separations. The scatter plots of the measured isotope abundance ratios for the painting pigments from P. P. Rubens, A. van Dyck and other Flemish painters exhibit a very narrow distribution forming a cluster. The range of the measured ratio 206 Pb/ 204 Pb amounts to 0.55% and for the ratio 207 Pb/ 204 Pb to 0.2%. The comparison of the data to cis-alpine (Italian) sample pigments from paintings from the same time period reveals a clear distinction between the two fields. With respect to the lead isotope data originating from the ores it is assumed that the pigment isotope ratio distribution can be explained by very distinct origin of raw materials. Presumably, no mixing of different lead ores from Europe took place. The comparison of the measured white lead isotope ratio values (Flemish paintings) and the data from ore samples led to the unexpected conclusion that local ores were not used for the pigment production but British or German sources. 1. Introduction The pigment lead white, a basic lead carbonate, has been produced and used since ancient times as a main component in white paint. Its prominent characteristics are the excellent light fastness and its rapid drying capabilities when used in combination with an oil such as linseed or walnut oil. Because of its toxicity it had generally been replaced by zinc and titanium pigments in the 19th and 20th centuries, respectively. Natural lead consists of four isotopes, 204 Pb, 206 Pb, 207 Pb and 208 Pb. The last three isotopes derive partly from the radioactive decay of the nuclides of uranium ( 238 U and 235 U) and thorium ( 232 Th). 204 Pb, however, is not radiogenic and therefore its concentration is constant in time. The use of lead isotope ratios for authentication and provenance investiga- tions depends on a two-fold coincidence: (i) Geologically, lead is one of the few chemical elements which varies markedly in its isotopic composition. The parameters on which the isotopic composition primarily depend are the age, the U/Pb and Th/Pb amount content ratios of the rock units from which fluids extracted lead to form ore deposits. 1 (ii) Historically, lead was among the first metals extracted from ores by man, and because it is abundant in nature and relatively inexpensive, lead is found on a great many archaeological sites. The principle of the lead isotope ratio technique for the determina- tion of the origin of the samples and the paintings, respec- tively, is the comparison of the data acquired from the analysis of lead white pigments and the geological lead ore samples. Geochemical properties (trace element content, isotope abundance ratios) have been used as a tool to establish the provenance of artifacts. 2–9 Relying on trace elements alone may have several drawbacks since an artifact is rarely made up of a chemically homogenous material. The chemical composi- tion of a sample taken from an artifact can furthermore be influenced by the impurities due to the addition of fluxes in the smelting process or fractionation of main and trace elements during the cooling process. 10 Constraints on the use of lead isotope data for provenancing are given by the potential blending of the raw products, which might originate from different sources. Furthermore, a full separation of the origin for lead isotope ratio ore field data is not given in any case, so an artifact can not be traced to one specific origin. Due to the variability of the isotope ratios of a given ore field a further contribution of uncertainty has to be considered. 11 The lead isotope ratios are not noticeably altered by processing lead ores to refined products. This is a basic condition when using lead isotope abundance ratios for provenance studies, and therefore the comparability of results for different artifacts is guaranteed. PAPER www.rsc.org/analyst | The Analyst 898 | Analyst, 2005, 130, 898–906 This journal is ß The Royal Society of Chemistry 2005 Downloaded on 14 January 2013 Published on 15 April 2005 on http://pubs.rsc.org | doi:10.1039/B418105K View Article Online / Journal Homepage / Table of Contents for this issue