Nineteenth century chrome yellow and chrome deep from Winsor & NewtonTM |
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| Authors: | Vanessa Otero Joana V Pinto Leslie Carlyle Márcia Vilarigues Marine Cotte |
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| Institution: | 1. Department of Conservation and Restoration and LAQV-REQUIMTE, Faculty of Sciences and Technology, Universidade NOVA de Lisboa, Monte da Caparica, Portugal;2. CENIMAT/I3N, Material Science Department, Faculty of Sciences and Technology, Universidade NOVA de Lisboa, Monte da Caparica, Portugal;3. Department of Conservation and Restoration and VICARTE, Faculty of Sciences and Technology, Universidade NOVA de Lisboa, Monte da Caparica, Portugal;4. European Synchrotron Radiation Facility, Grenoble, France;5. Laboratoire d'Archéologie Moléculaire et Structurale, Paris, France |
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| Abstract: | The Winsor & NewtonTM (W&N) nineteenth century archive database includes digitised images of hand-written instructions and workshop notes for the manufacture of their artists’ materials. For the first time, all 183 production records for yellow lead chromate pigments were studied and evaluated. They revealed that W&N produced essentially three pigment types: lemon/pale based on mixed crystals of lead chromate and lead sulphate Pb(Cr,S)O4]; middle on pure monoclinic lead chromate PbCrO4]; and deep that contains the latter admixed with basic lead chromate Pb2CrO5]; accounting for 53, 22, and 21% of the production, respectively. Production records for primrose (4%) were also included since the formulation results in mixed crystals with a high percentage of lead sulphate, which, according to the literature, leaves it more prone to degradation. Each pigment type is characterised by only one or two main synthetic pathways; process variations reveal a systematic and thorough search for a high-quality durable product. A comparison of the chemical composition of pigment reconstructions with early W&N oil paint tubes showed that their records entitled ‘pale’ and ‘lemon’ correlated with the pigment in their tube labelled chrome yellow and, ‘middle’ and ‘deep’ with the label chrome deep. Lemon and middle pigment formulations were made into oil paints to assess their relative photo-stability. The degradation process was followed by colorimetry and was studied by synchrotron radiation-based techniques. Based on the X-ray absorption spectroscopy data, the possibility for creating a stability index for chrome yellows is discussed. |
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| Keywords: | Chrome yellow Lead chromate Reconstructions Winsor & NewtonTM µ-Fourier-transform infrared spectroscopy (µ-FTIR) Synchrotron radiation (SR)-based techniques X-ray absorption near-edge microspectroscopy (µ-XANES) |
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