Composition and microstructure of the lead white pigment in Masters paintings using HR Synchrotron XRD ☆ V. Gonzalez a,b, ⁎, T. Calligaro a,b , G. Wallez a,b,c , M. Eveno a , K. Toussaint a,b , M. Menu a,b a Centre de Recherche et de Restauration des Musées de France, C2RMF, Palais du Louvre, 75001 Paris, France b PSL Research University, Chimie ParisTech-CNRS, Institut de Recherche de Chimie Paris, UMR8247, 75005 Paris, France c Sorbonne University, UPMC Univ. Paris 06, France abstract article info Article history: Received 10 July 2015 Received in revised form 2 November 2015 Accepted 2 November 2015 Available online 11 November 2015 Keywords: Lead white Synchrotron diffraction Rietveld Cerussite Hydrocerussite Paintings Fifteen lead white-containing painting samples, about 1–3 μg in weight, from a selection of easel painting mas- terpieces of the Louvre and other French museums, dating from the Renaissance to the late 19 th century, were investigated using synchrotron diffraction on the ESRF high resolution XRD beamline ID22. The Rietveld analysis revealed the nature of the pigments through the cerussite:hydrocerussite (PbCO 3 :Pb 3 (CO 3 ) 2 (OH) 2 ) ratios, the approximate dimensions of the crystallites and the presence of crystalline extenders. This first insight into a still widely unknown domain gives some hints, but also raises questions about the artists' preferences for selecting, preparing and post-treating white pigments. A significant increase of the crystallites size over five cen- turies also suggests an evolution of these processes. © 2015 Elsevier B.V. All rights reserved. 1. Introduction From the Renaissance to the 20 th c., easel paintings contain various pigments dispersed in an organic matrix. Among them, lead white was omnipresent, in the ground layers as well as in the pictorial layers, sometimes mixed with other colors [1]. Lead white consists in a mixture of cerussite PbCO 3 (C) and hydrocerussite Pb 3 (CO 3 ) 2 (OH) 2 (HC) that present different crystallographic features. Cerussite has an ortho- rhombic (space group Pmcn) aragonite-type structure, a = 5.179 Å, b = 8.492 Å, c = 6.141 Å [2]. Though its morphology can vary a lot [3], it is most generally elongated along the [100] direction. Rhom- bohedral (R-3 m) hydrocerussite, with lattice parameters a = 5.246 Å, c = 23.702 Å [4], tends to crystallize as hexagonal platelets. However, morphologies (sizes and shapes) of cerussite and hydrocerussite crys- tallites can markedly vary [5]. The manufacturing of lead white remained almost unchanged since the Antiquity (when it was mostly used as a cosmetic [6] until the 19 th c). The synthesis process, although used in all Europe was particularly developed in The Netherlands at the end of the 16 th c., hence its name of “Dutch process” [7]. It was based on the corrosion of lead: metal sheets were placed into jars, above acetic acid (vinegar). The jars were then covered up by horse manure, and left to rest for 20 to 90 days. Several rows of jars could be stacked up, so the name “stack-process” was often associated with the lead white synthesis. While the acetic acid va- pors led to the formation of lead acetate, the decomposition of the ma- nure produced heat and carbon dioxide that allowed the formation of cerussite PbCO 3 and hydrocerussite Pb 3 (CO 3 ) 2 (OH) 2 . Historical treatises reveal that several lead white qualities were proposed by the manufac- turers, at very different prices [8,9]. Questions remain as to what consti- tuted those various qualities, and how they were obtained. In particular, many post-synthesis treatments were commonly applied, among which the washing, grinding of the pigment in water or in acidic medium (vinegar), the heating in water, the levigation in order to select pigment particles according to their size [10]. Painters then mixed the mineral powder with an organic binder and other pigments of their choice, be- fore using the paint. Starting from the 18 th c., the development of modern chemistry led to the multiplication of the synthesis processes [11]. The corrosion of metallic lead responsible for the carbonates formation could take place in dry as well as in aqueous environment. As a result, an even larg- er variety of lead white qualities was proposed. It can be noted that the results of those multiple researches of new synthesis processes were unsuccessful: the general consensus at the beginning of the 20 th c., be- fore its selling was prohibited because of its toxicity, was that no lead white synthesized by “modern” ways came close in quality to that ob- tained by the Dutch process. Microchemical Journal 125 (2016) 43–49 ☆ Selected papers presented at TECHNART 2015 Conference, Catania (Italy), April 27– 30, 2015. ⁎ Corresponding author at: Centre de Recherche et de Restauration des Musées de France, C2RMF, Palais du Louvre, 75001 Paris, France. E-mail address: victor.gonzalez@culture.gouv.fr (V. Gonzalez). http://dx.doi.org/10.1016/j.microc.2015.11.005 0026-265X/© 2015 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Microchemical Journal journal homepage: www.elsevier.com/locate/microc