## 4 Discussion
#### Implications for Art Conservation  
Several purportedly azeotropic solvent mixtures have been suggested as viable alternatives to aromatic solvents that exhibit moderate toxicity and have, in certain instances, demonstrated efficacy in the removal of dirt and overpaint or the reduction in aged, discolored varnish (2008); [PERSON] _et al._ (2010); [PERSON] _et al._ (2012); [PERSON] _et al._ (2012); [PERSON] _et al._ (2012). These solvent mixtures have been drawn from the literature by noting azeotropes containing solvents whose combined solubility parameters seem like they would be effective at removing prime and aged organic coatings. However, the compositions of azeotropes are typically provided in the chemical literature at boiling temperatures far from the room temperature conditions where they are utilized in conservation studios. As previously shown, in the context of the isopropanol and n-hexane system, the deviation in azeotropic composition between boiling and ambient temperature is substantial. This divergence, on the order of 10% v/v in isopropanol concentration, could have significant implications for art conservators depending on the specific nature of the materials being solubilized, or conversely the artwork components they wish to leave unscathed. For illustration, if a conservator operates assuming that the azeotropic composition is 19% v/v isopropanol at room temperature, the solution will experience an enrichment in isopropanol concentration as evaporation occurs. It is important to recognize that isopropanol is characterized as a more potent solvent in the context of solubilizing shellac, as corroborated by prior studies [PERSON] _et al._ (2012); [PERSON] _et al._ (2012), and so the changing mixture will become a better solvent for those coatings as it evaporates. In contrast, utilizing an azeotropic mixture with an accurate isopropanol concentration of 10% v/v for the cleaning of artworks may yield an insufficiently robust solvent system to achieve the desired efficacy in its application, even if it will evaporate at constant composition, although this has not been tested by the authors. Regardless of the question of potency, the main argument for the use of azeotropes in conservation treatment, i.e., that they will remain constant in composition over the course of their evaporation, is questionable. With the isopropanol and n-hexane system, the boiling point azeotrope mixture would clearly behave zeotropically under conditions of room temperature evaporation; however, for the 2-butanone and cyclohexane system, the composition would remain somewhat consistent since there is not a significant dependence on temperature or pressure. In pursuit of furnishing more insightful azeotropic data, we estimated in Table 3 the azeotropic composition for an array of previously determined potential azeotropic mixtures that hold relevance in art conservation [PERSON] _et al._ (2012) using the mathematical methodology previously indicated [PERSON] _et al._ (2012). The estimations encompass boiling, room temperature (-21 \({}^{\circ}\)C), and an arbitrary azeotropic pressure of 100 mmHg. Three principal facets warrant attention in this discussion. First, azeotropic mixtures composed of alcohol (e.g., isopropanol) and a hydrocarbon (i.e., n-hexane) tend to exhibit pressure sensitivity, leading to fluctuations in their azeotropic composition. It is imperative to recognize and account for these alterations, especially in scenarios where an elevated concentration of alcohol is necessitated for its ability to solubilize or swell a coating material during removal. Along similar lines, it is notable that azeotropic mixtures composed of two non-alcoholic solvents do not generally experience significant variations in their azeotropic composition under disparate pressure conditions. Consequently, these mixtures exhibit an attribute that is decidedly advantageous for art conservation purposes, as their concentration remains relatively consistent during evaporation at room temperature.