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Degradation of Cadmium Yellow Paint: New Evidence from Photoluminescence Studies of Trap States in Picasso's Femme ( Époque des "Demoiselles d'Avignon")

Artikel i vetenskaplig tidskrift
Författare Daniela Comelli
Douglas MacLennan
Marta Ghirardello
Alan Phenix
Catherine Schmidt Patterson
Herant Khanjian
Markus Gross
Gianluca Valentini
Karen Trentelman
Austin Nevin
Publicerad i Analytical Chemistry
Volym 91
Nummer/häfte 5
Sidor 3421-3428
ISSN 0003-2700
Publiceringsår 2019
Publicerad vid
Sidor 3421-3428
Språk en
Länkar https://doi.org/10.1021/acs.analche...
https://www.ncbi.nlm.nih.gov/pubmed...
Ämnesord Conservation of Art, Technical Art History, Conservation Science, Heritage Science
Ämneskategorier Materialkemi, Spektroskopi, Analytisk kemi

Sammanfattning

Paints based on cadmium sulfide (CdS) were popular among artists beginning in the mid-19th century. Some paint formulations are prone to degrade, discoloring and disfiguring paintings where they have been used. Pablo Picasso's Femme (Époque des "Demoiselles d'Avignon") (1907) includes two commercial formulations of CdS: one is visibly degraded and now appears brownish yellow, while the other appears relatively intact and is vibrant yellow. This observation inspired the study reported here of the photoluminescence emission from trap states of the two CdS paints, complemented by data from multispectral imaging, X-ray fluorescence spectroscopy, micro-FTIR, and SEM-EDS. The two paints exhibit trap state emissions that differ in terms of spectrum, intensity, and decay kinetics. In the now-brownish yellow paint, trap state emission is highly favored with respect to near band edge optical recombination. This observation suggests a higher density of surface defects in the now-brownish yellow paint that promotes the surface reactivity of CdS particles and their subsequent paint degradation. CdS is a semiconductor, and surface defects in semiconductors can trap free charge carriers; this interaction becomes stronger at reduced particle size or, equivalently, with increased surface to volume ratio. Here, we speculate that the strong trap state emission in the now-brownish cadmium yellow paint is linked to the presence of CdS particles with a nanocrystalline phase, possibly resulting from a low degree of calcination during pigment synthesis. Taken together, the results presented here demonstrate how photoluminescence studies can probe surface defects in CdS paints and lead to an improved understanding of their complex degradation mechanisms.

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