## 4 Discussion  
Conservation practices are constantly evolving, and the ethics of the field require that new treatment protocols be carefully evaluated so that their efficacy and impacts on the works of art are understood. To design the protocol for their treatment of the Braque painting, [PERSON] and [PERSON] first removed the lining canvas and conducted extraction trials by immersing weighed sections of the lining canvas in different solvents and used the pre- and post-extraction weight difference to determine which solvents were most effective in removing the wax-resin mixture, which was of an unknown composition [9]. They found that xylene and OMS were the most successful but were unable to determine what percentage of the wax-resin present was being removed, what components were being removed, and what was being left behind. As there were many different historical recipes for wax-resin mixtures, assessing the solubility of the wax-resin is an important first step; however, many resins oxidize and polymerize as they age, thus becoming more difficult to solubilize [25; 33; 34; 35; 36; 37; 38; 39]. The ability of TSP-GC/MS to identify resinous components would permit the analysis of pre- and post-extraction lining canvas fragments, thus revealing the efficacy of extraction of the different materials. Although not to be undertaken without sufficient reason, the small sample size required by this technique would also permit the analysis of the actual work of art itself. In an extraction process such as that used on the Braque [9], it is very valuable to be able to track what is being removed at different stages of the treatment process. Although quantitative pyrolysis GC/MS is difficult, the TSP-GC/MS analysis of the used Evolon sheets and the normalization of peak areas to a pyrolysis product of Evolon provided a facile means to account for variations in sample size and thus assess the relative removal of beeswax and dammar from the mock-up at different intervals in the extraction process. This approach also avoids the variability induced by the solubilization of materials from the Evolon sheets, an approach previously used to evaluate the extraction of oil paint components into Evolon [40]. In this experiment, the TSP-GC/MS results indicate that the beeswax and dammar were removed with relatively equivalent efficacy and that the majority of the wax-resin mixture was removed in the first three intervals. These findings were mirrored by colorimetry of the UV-induced visible fluorescence images, suggesting that this lower tech, more accessible approach can also be used to document the relative  
Figure 8: UV-induced visible fluorescence images of the used xylene-loaded Evolon sheets and Photoshop-derived Lab values for the sheets. The scale bar is an RMI Conservation Target. efficiency of different treatment intervals if the more complicated mass spectroscopic approach is not available; however, these approaches cannot track the differential removal of wax and resinous components in a mixture. These approaches are also incapable of measuring the small but detectable amounts of both beeswax and dammar that remained behind in the mock-up after the full process. As previously noted, aging and oxidative processes alter the solubilities of materials, including beeswax and dammar [25; 33; 41; 42]. The wax-resin mixture used on the mock-up was unaged, so the results seen for the protocol used in this test case may not be applicable to naturally aged mixtures containing the same components. Laser speckling imaging has shown that when the solvent-loaded Evolon is used to remove varnish layers, the varnish layer initially retards the interaction of the solvent with the paint layer [43]. As exposure times lengthen and the varnish is solubilized, the solvent migrates into the paint and increases the dynamics of that layer.