Assessment of the composition and condition of animation cels made from cellulose acetate

Cellulose diacetate and cellulose triacetate cels from animated feature films in the collection of the Walt Disney Animation Research Library were tested by several analytical techniques in order to assess their composition and look for evidence of degradation. Triphenyl phosphate and a range of phthalate plasticizers were identified using pyrolysis-gas chromatography/mass spectrometry, which also showed evidence that evaporation of more volatile plasticizers may have occurred. Plasticizer content measurements by solvent extraction, found to be more accurate than volatile content data from thermogravimetric analysis, revealed there was less residual plasticizer in triacetate cels compared to diacetate cels. Gas chromatography/mass spectrometry, performed to quantify the acetyl content of cels after removal of plasticizers by solvent extraction, revealed some evidence for hydrolysis of the oldest cels, although the reduction could be related to original variations in acetate content from the polymer manufacturers. Use of Fourier-transform infrared spectroscopy to measure deacetylation of the cellulose acetate polymer based on the hydroxyl to carbonyl peak area ratio proved less satisfactory. Moreover, because the cels cannot be measured directly due to interference from plasticizers, non-invasive assessment of deacetylation using a portable instrument would be impossible. The results from this analytical survey provide an important point of reference against which long-term changes in cel composition can be monitored. © 2014 The J. Paul Getty Trust. Published by Elsevier Ltd. All rights reserved

A multi-analytical study on the photochemical degradation of synthetic organic pigments

This paper summarizes the results of a photochemical ageing study on selected synthetic organic pigments used in paint formulations both as artists' and industrial materials. Some of them are rated by the American Society for Testing and Materials (ASTM) as fugitive. We performed an accelerated ageing test for the first time on the neat pigment powders, without any binder, to determine the lightfastness of the pure pigments. Several techniques were used to compare the aged and un-aged pigments: colorimetric measurements, Fourier transform infrared spectroscopy (FTIR), and pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS). Colorimetry highlighted a relevant change in colour (ΔE∗> 1) after the ageing treatment, whereas Fourier transform infrared spectroscopy technique allowed us to identify specific differences in absorption. Pyrolysis-gas chromatography/mass spectrometry showed different pyrolysis products in the aged pigments, with respect to the un-aged ones. © 2015 Elsevier Ltd

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

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