Degradation Process of Lead Chromate in Paintings by Vincent van Gogh Studied by Means of Synchrotron X-ray Spectromicroscopy and Related Methods. 2. Original Paint Layer Samples

详细信息    查看全文

• 作者：Letizia Monico ; Geert Van der Snickt ; Koen Janssens ; Wout De Nolf ; Costanza Miliani ; Joris Dik ; Marie Radepont ; Ella Hendriks ; Muriel Geldof ; Marine Cotte
• 刊名：Analytical Chemistry
• 出版年：2011
• 出版时间：February 15, 2011
• 年：2011
• 卷：83
• 期：4
• 页码：1224-1231
• 全文大小：1102K
• 年卷期：v.83,no.4(February 15, 2011)
• ISSN：1520-6882

文摘

The darkening of the original yellow areas painted with the chrome yellow pigment (PbCrO₄, PbCrO₄路xPbSO₄, or PbCrO₄路xPbO) is a phenomenon widely observed on several paintings by Vincent van Gogh, such as the famous different versions of Sunflowers. During our previous investigations on artificially aged model samples of lead chromate, we established for the first time that darkening of chrome yellow is caused by reduction of PbCrO₄ to Cr₂O₃路2H₂O (viridian green), likely accompanied by the presence of another Cr(III) compound, such as either Cr₂(SO₄)₃路H₂O or (CH₃CO₂)₇Cr₃(OH)₂ [chromium(III) acetate hydroxide]. In the second part of this work, in order to demonstrate that this reduction phenomenon effectively takes place in real paintings, we study original paint samples from two paintings of V. van Gogh. As with the model samples, in view of the thin superficial alteration layers that are present, high lateral resolution spectroscopic methods that make use of synchrotron radiation (SR), such as microscopic X-ray absorption near edge (渭-XANES) and X-ray fluorescence spectrometry (渭-XRF) were employed. Additionally, 渭-Raman and mid-FTIR analyses were carried out to completely characterize the samples. On both paint microsamples, the local presence of reduced Cr was demonstrated by means of 渭-XANES point measurements. The presence of Cr(III) was revealed in specific areas, in some cases correlated to the presence of Ba(sulfate) and/or to that of aluminum silicate compounds.