Scanning X-ray fluorescence spectroscopy and micro-X-ray absorption near-edge structure analysis as a guiding tool for the conservation treatment of two eighteenth-century Philadelphian portraits
An in-depth technical examination and conservation treatment of paintings by William Williams (Bristol 1727–1791 Bristol) has shed light on the artist's materials and technique. This investigation centered primarily on Williams's two 1766 portraits of William and David Hall. The paintings are considered the earliest life-sized, full-length portraits executed in the Philadelphia area. The analysis of the artist's palette indicated deliberate choices in the use of orpiment (As2S3). The mineral's tendency to oxidize to colorless and water-soluble arsenic oxides likely caused color changes and degraded organic binder in the orpiment-rich areas. μ-XANES revealed orpiment photodegradation to arsenate species at the paint surface, with migration to the ground layers. Just below the paint surface, arsenic remains bound primarily as arsenite, with some associated with sulfur as orpiment. This As distribution suggests that the paint is liable to further degradation by photooxidation and use of moisture would be detrimental. Given this treatment-critical degradation phenomenon, it was important to identify all arsenic-containing areas of both portraits. Scanning XRF allowed rapid and accurate collection of maps from both portraits. Elemental maps of arsenic identified the orpiment-rich areas of the painting, which would be susceptible to further degradation upon exposure to water during treatment. An aqueous adhesive was necessary to consolidate the cupped paint of the glue-paste lined paintings. The arsenic maps guided the use of two different consolidants–BEVA 371 for the water-sensitive orpiment-rich paint and sturgeon glue for all other areas, striking a compromise between esthetic improvement and long term preservation.
This is the peer reviewed version of the following article: Porell, M., Cushman, M., Fischel, J. S. T., Fischel, M. H. H., Sparks, D. L., Grayburn, R., X-Ray Spectrom 2023, 1. https://doi.org/10.1002/xrs.3345, which has been published in final form at https://doi.org/10.1002/xrs.3345. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Use of Self-Archived Versions. This article may not be enhanced, enriched or otherwise transformed into a derivative work, without express permission from Wiley or by statutory rights under applicable legislation. Copyright notices must not be removed, obscured or modified. The article must be linked to Wiley’s version of record on Wiley Online Library and any embedding, framing or otherwise making available the article or pages thereof by third parties from platforms, services and websites other than Wiley Online Library must be prohibited. © 2023 John Wiley & Sons Ltd. This article will be embargoed until 04/02/2024.
arsenic speciation, paintings conservation, scanning XRF, μ-XANES
Porell, M., Cushman, M., Fischel, J. S. T., Fischel, M. H. H., Sparks, D. L., Grayburn, R., X-Ray Spectrom 2023, 1. https://doi.org/10.1002/xrs.3345