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Chemical Mapping by Macroscopic X‐ray Powder Diffraction (MA‐XRPD) of Van Gogh's Sunflowers : Identification of Areas with Higher Degradation Risk
Author(s) -
Vanmeert Frederik,
Hendriks Ella,
Van der Snickt Geert,
Monico Letizia,
Dik Joris,
Janssens Koen
Publication year - 2018
Publication title -
angewandte chemie international edition
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 5.831
H-Index - 550
eISSN - 1521-3773
pISSN - 1433-7851
DOI - 10.1002/anie.201713293
Subject(s) - monoclinic crystal system , orthorhombic crystal system , powder diffraction , crystallography , crystallite , pigment , materials science , x ray crystallography , diffraction , crystal structure , chemistry , mineralogy , optics , physics , organic chemistry
Abstract The discoloration rate of chrome yellow (CY), a class of synthetic inorganic pigments (PbCr 1− x S x O 4 ) frequently used by Van Gogh and his contemporaries, strongly depends on its sulfate content and on its crystalline structure (either monoclinic or orthorhombic). Macroscopic X‐Ray powder diffraction imaging of selected areas on Van Gogh's Sunflowers (Van Gogh Museum, Amsterdam) revealed the presence of two subtypes of CY: the light‐fast monoclinic PbCrO 4 (LF‐CY) and the light‐sensitive monoclinic PbCr 1− x S x O 4 ( x ≈0.5; LS‐CY). The latter was encountered in large parts of the painting (e.g., in the pale‐yellow background and the bright‐yellow petals, but also in the green stems and flower hearts), thus indicating their higher risk for past or future darkening. Overall, it is present in more than 50 % of the CY regions. Preferred orientation of LS‐CY allows observation of a significant ordering of the elongated crystallites along the direction of Van Gogh's brush strokes.