{'fraction_non_alphanumeric': 0.021869382863990414, 'fraction_numerical': 0.005092869982025165, 'mean_word_length': 4.8578947368421055, 'pattern_counts': {'":': 0, '<': 0, '<?xml version=': 0, '>': 0, 'https://': 0, 'lorem ipsum': 0, 'www.': 1, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
USING XRF FOR SEMI-QUANTITATIVE ANALYSIS IN A STUDY OF DELAMINATING PAINT

This paper describes the elemental analysis performed as part of an investigation into the cause of paint delaminating from the ground in some modern paintings. Paintings are very complex systems and there are many variables to consider when determining the cause of any delamination. Composite samples of oil or alkyd paints, over acrylic grounds, were prepared in the lab. Samples were naturally aged for eight years, and some of the samples delaminated. Initial examinations with a hand-held X-ray fluorescence (XRF) unit indicated that zinc could be the common factor in the delaminating samples. The XRF unit has several modes of operation, and corresponding algorithms to interpret the results; however, none of these modes is appropriate for artists’ materials. The resulting percentages were clearly incorrect. There was not enough material in some of the samples and particularly in the actual paintings examined to allow for destructive testing of all the different paints. More accurate results were required, so where possible, samples were analyzed by the destructive inductively coupled plasma (ICP) method. The XRF spectra of the same samples were integrated and the results compared to the ICP results. Calibration curves for lead and zinc in paint were prepared. The equations from these curves were then used to calculate the percentage of zinc and lead in the other samples and in actual paintings, which could only be analyzed by non-destructive methods because of the limited amount of sample. The accuracy of this method was found to be limited by the thickness of the paint layer. The results of this project showed that almost all delaminating samples and paintings contained zinc. The severely delaminating paintings contained high percentages of zinc (~16-20%). The zinc and lead calibration curves can now be used to calculate approximate percentages of those elements in any paintings examined by XRF in the future. INTRODUCTION Painting in oil or alkyd over acrylic is usually considered a safe practice. In some cases, however, there is severe delamination within just a few months or a few years of painting a work of art. Figure 1 is an example of a painting completely destroyed by delamination. The first image was taken shortly after the painting was completed; the second is a detail showing its currant condition, where most of the blue paint has flaked off and some of the green paint is missing as well. A project is currently in progress investigating the cause of such delaminations. Early on in this process it became clear that zinc in the oil paint could be a significant factor. The presence of zinc can be easily determined with x-ray fluorescence (XRF). The Queen’s University art conservation program owns a hand-held XRF, which has been very useful as a non-destructive and very quick method of identifying elements in art objects. For this project identification was not enough, since it was expected that quantities of zinc (or other metals) could be related to the number of samples delaminating or the degree of delamination in an actual painting. 9th International Conference on NDT of Art, Jerusalem Israel, 25-30 May 2008 For more papers of this publication click: www.ndt.net/search/docs.php3?MainSource=65