van Loon et al. Herit Sci (2017) 5:26 DOI 10.1186/s40494-017-0138-1 RESEARCH ARTICLE Open Access Artifcial orpiment, a new pigment in Rembrandt’s palette Annelies van Loon1,2* , Petria Noble1, Anna Krekeler1, Geert Van der Snickt3, Koen Janssens3, Yoshinari Abe4, Izumi Nakai4 and Joris Dik2 Abstract This paper reports on how the application of macro X-ray fuorescence (MA-XRF) imaging, in combination with the re-examination of existing paint cross-sections, has led to the discovery of a new pigment in Rembrandt’s palette: artifcial orpiment. In the NWO Science4Arts ‘ReVisRembrandt’ project, novel chemical imaging techniques are being developed and applied to the study of Rembrandt’s late paintings in order to help resolve outstanding questions and to gain a better understanding of his late enigmatic painting technique. One of the selected case studies is the Portrait of a Couple as Isaac and Rebecca, known as ‘The Jewish Bride’, dated c. 1665 and on view in the Rijksmuseum. During the re-installation of the Rijksmuseum in 2013, the picture was scanned using the Bruker M6 Jetstream MA- XRF scanner. The resulting elemental distribution maps made it possible to distinguish many features in the painting, such as bone black remains of the original hat (P, Ca maps), and the now discolored smalt-rich background (Co, Ni, As, K maps). The arsenic (As) map also revealed areas of high-intensity in Isaac’s sleeve and Rebecca’s dress where it could be established that it was not related with the pigment smalt that also contains arsenic. This pointed to the presence of a yellow or orange arsenic-containing pigment, such as realgar or orpiment that is not associated with the artist’s palette. Subsequent examination of existing paint cross-sections from these locations taken by Karin Groen in the 1990s identifed isolated, almost perfectly round particles of arsenic sulfde. The round shape corresponds with published fndings on a purifed form of artifcial orpiment glass obtained by dry processing, a sublimation reaction. In bright feld, the particles characteristically exhibit a dark cross in the middle caused by internal light refections. The results of additional non-invasive techniques (portable XRD and portable Raman) are discussed, as well as the implica- tions of this fnding and how it fts with Rembrandt’s late experimental painting technique. Keywords: Painting analysis, MA-XRF imaging, Cross-sections, Rembrandt, The Jewish Bride, Artifcial orpiment Background materials to combine, in order to achieve his intended Te production of pigments was the work of special- painterly efects and pictorial illusion, while manipulating ists in the seventeenth century. Tere was a lively trade color contrast, texture and translucency of the paint. ‘His in pigments and other painting materials throughout mixtures attain an almost comical level of complexity’, Europe at the time. Artists bought their materials at an as Philip Ball rightly pointed out in his book in 2003 [3]. apothecary’s shop or at a grocer or colorman [1, 2]. Te Furthermore, Rembrandt deliberately exploited all stages choice of pigments was limited, as compared to the huge of the painting process in the fnal image: from ground selection of pigments available today. But this limited to painted sketch to underpaint, to the fnal paint layers. palette was by no means an obstacle for their creativity. Rembrandt’s late works (after 1651) show a fundamen- In particular an artist like Rembrandt knew exactly which tal change in the means with which he created pictorial illusion [4]. Tese works are characterized by their loose, sketchy appearance and unusual surface roughness. To *Correspondence: [email protected] realize these efects, this demanded new ways to apply 1 Rijksmuseum Amsterdam, Hobbemastraat 22, Postbox 74888, 1070 DN Amsterdam, The Netherlands the paint in order to manipulate its properties. Rem- Full list of author information is available at the end of the article brandt started to use a palette knife to spread his paint, © The Author(s) 2017. This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/ publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated. van Loon et al. Herit Sci (2017) 5:26 Page 2 of 13 modelled his paint to attain texture, and scratched in the [12]. Notably, the resulting arsenic (As) map revealed paint with the back of his brush or used his fnger [5, 6]. areas of high-intensity in Isaac’s sleeve and Rebecca’s Te use of thickly impastoed, lead white passages, usually dress where it could be established that it was not related remarkably well preserved, are common throughout his with the pigment smalt that also contains arsenic. Te entire oeuvre. In the late works Rembrandt also used lead data-processing also corrects for overlap of the As–K white paint in underlayers to build up the impasto, which emission lines with spectral lines of lead and mercury. were then toned in the fnal layers [7]. Te dense packing Tis pointed to the presence of a yellow or orange-red of the pigment particles primarily accounts for the stif- arsenic-containing pigment, such as orpiment (As 2S3) or ness of the lead white paint that remains standing after realgar (As4S4) that is currently not associated with the application. Groen also identifed the addition of a gum artist’s palette [13]. in passages of red lakes, thought to have been added to In the seventeenth century, lead–tin yellow, yellow thicken the paint. Another unique feature of Rembrandt’s ochre and yellow lake were the dominant yellows in late painting technique is the extensive use of coarse Northern European easel painting, whereas vermilion, smalt, a blue cobalt glass [8, 9]. He often mixed smalt red ochre and red lake were the dominant reds. Orpi- with lakes, earths and black pigments, not only for its ment and realgar were less frequently used, with the color, but also for its drying properties and to give texture exception of still-life painting. Although their rich color and translucency to the paint. It is not always clear to us was universally praised in treatises, they had well-known what Rembrandt’s intentions were, since many of his late disadvantages. Besides their poisonous character, they pictures have severely changed in appearance over time, were poor drying, lacked body, and were difcult to grind as a result of paint alterations and old restorations. and handle. Sources also mention incompatibility with In the NWO Science4Arts ‘ReVisRembrandt’ project, other pigments. novel chemical imaging techniques are being developed To be able to confrm and identify the arsenic pigment and applied to the study of Rembrandt’s late paintings in Te Jewish Bride, we correlated the results of the MA- in order to gain a better understanding of his late enig- XRF scanning with the re-examination of existing paint matic painting technique, and to help resolve outstand- cross-sections taken during the restoration of the paint- ing questions regarding attribution, paint alterations, ing in the 1990s. In-situ spot analyses were carried out artist’s changes and old restorations [6, 10]. Techniques at the same time in the galleries using portable X-ray include macro X-ray fuorescence imaging (MA-XRF), difraction (XRD) and Raman spectroscopy. Tis paper refectance imaging spectroscopy (RIS), macro X-ray presents the results of analysis, and discusses the impli- powder difraction (MA-XRPD), as well as optical coher- cations of the identifcation of a new pigment in Rem- ence tomography (OCT). One of the selected case studies brandt’s palette. is the Portrait of a Couple as Isaac and Rebecca, known as ‘Te Jewish Bride’, dated c. 1665 that is on view in the Experimental Rijksmuseum (Fig. 1a). Te painting owes its name to Non‑invasive techniques the Amsterdam art collector Adriaan van der Hoop, who MA‑XRF purchased the painting in 1833. He believed that it shows Macroscopic X-ray fuorescence maps were collected a Jewish father hanging a necklace around the neck of his using a Bruker M6 Jetstream instrument [14]. Te instru- daughter on her wedding day. Today, the general consen- ment consists of a measuring head with a Rhodium-target sus is that the painting is a wedding portrait, depicting microfocus X-ray tube (30 W, maximum voltage 50 kV, a contemporary couple dressed in historical costumes maximum current 0.6 mA), and a 30 mm2 XFlash silicon as characters from the Old Testament. Te costumes are drift detector (SDD) with beryllium window (energy res- based on ffteenth- and sixteenth-century styles. Rem- olution <145 eV at Mn–Ka). By slowly moving the meas- brandt preferred these elaborate costumes over contem- uring head on the XY-motorized stage, the painting was porary classical draperies, probably because they gave scanned pixel by pixel, line by line. By recording the emit- him more opportunity to live out his rich imagination ted X-ray fuorescence radiation, the chemical elements and taste for colorful decorations [11]. Te story of Isaac present in the paint, which are associated with specifc and Rebecca was a popular theme associated with wed- pigments, could be identifed. Te beam size is defned dings and portraits of married couples in the seventeenth by means of a polycapillary optic with a focal spot of c. century. During the re-installation of the Rijksmuseum 40 µm.