Degradation Process of Lead Chromate in Paintings by Vincent van Gogh Studied by Means of Spectromicroscopic Methods. 3. Synthesis, Characterization, and Detection of Different Crystal Forms of the Chrome Yellow Pigment

Abstract

The painter, Vincent van Gogh, and some of his contemporaries frequently made use of the pigment chrome yellow that is known to show a tendency toward darkening. This pigment may correspond to various chemical compounds such as PbCrO(4) and PbCr(1-x)S(x)O(4), that may each be present in various crystallographic forms with different tendencies toward degradation. Investigations by X-ray diffraction (XRD), mid-Fourier Transform infrared (FTIR), and Raman instruments (benchtop and portable) and synchrotron radiation-based micro-XRD and X-ray absorption near edge structure spectroscopy performed on oil-paint models, prepared with in-house synthesized PbCrO(4) and PbCr(1-x)S(x)O(4), permitted us to characterize the spectroscopic features of the various forms. On the basis of these results, an extended study has been carried out on historic paint tubes and on embedded paint microsamples taken from yellow-orange/pale yellow areas of 12 Van Gogh paintings, demonstrating that Van Gogh effectively made use of different chrome yellow types. This conclusion was also confirmed by in situ mid-FTIR investigations on Van Gogh's Portrait of Gauguin (Van Gogh Museum, Amsterdam).

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

“…Two different ground layers were more accurately identified: the first one (innermost) contains mainly hydrocerussite with sphalerite and barite on which a very thin second layer containing hydrocerussite and barite with grains of anglesite is applied. The presence of sphalerite and barite together suggests the use of lithopone, a co-precipitate of BaSO 4 and ZnS introduced in 1874. The first layer may be a commercial ground, while the second has probably been prepared and applied by Matisse himself.…”

“…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.…”

“…Combining these observations with the results from artificially degraded mock-ups and supplementary time-of-flight-secondary ion mass spectrometry (ToF-SIMS) analyses of the surface of the painting samples, a preliminary degradation mechanism was suggested. The photo-oxidation of the CdS pigment was proposed to generate CdO, CdSO 4 , and SO 2 gas, which in high relative humidity environments, convert to H 2 SO 4 resulting in acid hydrolysis of the paint binding medium.…”

“…In the case of Still Life with Cabbage by James Ensor [7], the degradation of yellow CdS was related to the photo-oxidation of the cadmium sulphide to (hydrated) cadmium sulphate (CdSO 4 ÁnH 2 O). Repeated hydration and drying of the paint surface resulted in the formation of a thin (a few microns thick) layer of semi-transparent whitish globules of CdSO 4 ÁnH 2 O on the surface of the CdS-based paint. Another notable finding of this study was the identification of (NH 4 ) 2 ÁCd 2 (SO 4 ) 3 in the pigment layer, thought to be related to a previous aggressive cleaning treatment with dilute ammonia.…”

PbCrO4 yellow-pigment nanorods: An efficient and stable visible-light-active photocatalyst for O2 evolution and photodegradation

“…Lead chromate (PbCrO 4 ), one of the most commonly used inorganic yellow pigments in plastics, coatings and paints, could be a good visible-light-active photocatalyst due to its excellent photostability, thermostability, easy preparation and low cost [16][17][18]. Herein, using a simple precipitation reaction, we transformed heavy-metal Pb(II) and Cr(VI) pollutants into the yellow pigment, PbCrO 4 , as a stable and efficient visible-light-active photocatalyst for O 2 evolution from water with negligible pollutant residues during the photocatalytic reaction.…”