Degradation Process of Lead Chromate in Paintings by Vincent van Gogh Studied by Means of Synchrotron X-ray Spectromicroscopy and Related Methods. 1. Artificially Aged Model Samples

Abstract

On several paintings by artists of the end of the 19th century and the beginning of the 20th Century a darkening of the original yellow areas, painted with the chrome yellow pigment (PbCrO(4), PbCrO(4)·xPbSO(4), or PbCrO(4)·xPbO) is observed. The most famous of these are the various Sunflowers paintings Vincent van Gogh made during his career. In the first part of this work, we attempt to elucidate the degradation process of chrome yellow by studying artificially aged model samples. In view of the very thin (1-3 μm) alteration layers that are formed, high lateral resolution spectroscopic methods such as microscopic X-ray absorption near edge (μ-XANES), X-ray fluorescence spectrometry (μ-XRF), and electron energy loss spectrometry (EELS) were employed. Some of these use synchrotron radiation (SR). Additionally, microscopic SR X-ray diffraction (SR μ-XRD), μ-Raman, and mid-FTIR spectroscopy were employed to completely characterize the samples. The formation of Cr(III) compounds at the surface of the chrome yellow paint layers is particularly observed in one aged model sample taken from a historic paint tube (ca. 1914). About two-thirds of the chromium that is present at the surface has reduced from the hexavalent to the trivalent state. The EELS and μ-XANES spectra are consistent with the presence of Cr(2)O(3)·2H(2)O (viridian). Moreover, as demonstrated by μ-XANES, the presence of another Cr(III) compound, such as either Cr(2)(SO(4))(3)·H(2)O or (CH(3)CO(2))(7)Cr(3)(OH)(2) [chromium(III) acetate hydroxide], is likely.

2D X-ray and FTIR micro-analysis of the degradation of cadmium yellow pigment in paintings of Henri Matisse

“…Several examples of the discoloration of synthetic yellow pigments from the turn of the twentieth century (e.g. zinc yellow (K 2 OÁ4ZnCrO 4 Á3H 2 O) [1], chrome yellow (PbCrO 4 ) [2][3][4][5][6], and cadmium yellow (CdS) [7,8]) have been recently reported.…”

Nanoscale Investigation of the Degradation Mechanism of a Historical Chrome Yellow Paint by Quantitative Electron Energy Loss spectroscopy Mapping of Chromium Species

“…[1] Chrome yellows are often encountered in paintings from the end of 19th Century, such as in Falling leaves (Les Alyscamps) by van Gogh (1853-1890), [2,3] but also in works by Seurat (1859-1891) [4] and others. They are known to be sensitive towards darkening when exposed to sunlight.…”

“…Understanding the alteration processes of the pigments is of key importance both to (re)assess/ optimize the conditions in which works of art are stored and/ or to allow selection of appropriate restoration treatments. [1,7] In previous studies, artificial aging of lead chromate based compounds were performed through (a combination of) UV/ Vis light, heat, contaminants, [5,[8][9][10] and atmospheric gases (such as SO 2 [10] or H 2 S [11] ). By means of X-ray absorption nearedge structure (XANES) measurements at the micrometer scale, we previously demonstrated that the alteration of chromium yellow is associated with the reduction of the original Cr VI centers to Cr III .…”

“…By means of X-ray absorption nearedge structure (XANES) measurements at the micrometer scale, we previously demonstrated that the alteration of chromium yellow is associated with the reduction of the original Cr VI centers to Cr III . [1,6] Recently, Casadio and Rose characterized painting materials used by Picasso through XRF nanoprobe measurements; [12] the same authors also studied zinc-potassium chromate compounds in a painting by Seurat. [7] However, almost no other studies have been carried out to investigate at the nanoscale level the exact nature of the progression of the alteration mechanism of chrome yellows; nevertheless such information could yield more detailed insights into the sequence of chemical transformations that drive the degradation process, thereby providing additional and/or complementary information with respect to the knowledge already acquired at the microscale level by synchrotron radiation-based XANES methods.…”

“…[7] However, almost no other studies have been carried out to investigate at the nanoscale level the exact nature of the progression of the alteration mechanism of chrome yellows; nevertheless such information could yield more detailed insights into the sequence of chemical transformations that drive the degradation process, thereby providing additional and/or complementary information with respect to the knowledge already acquired at the microscale level by synchrotron radiation-based XANES methods. [1,3,13] Herein, advanced methods of quantitative scanning transmission electron microscopy (STEM) and electron energy loss spectroscopy (EELS) were employed to perform such a nanoscopic investigation on a sample of historical chrome yellow paint, dating back to the late 19th century that was already well characterized by means of XANES and other techniques. [1,3,6] The chemical and structural variations in this material were investigated before and after an artificial aging treatment with UVA/Vis light.…”