Art conservators use solvent mixtures to safely and selectively remove yellowed varnish from artworks and discolored overpaint from the surface of oil paintings, among many other applications. The differential evaporation rates for the solvents used in these cleaning mixtures can change the dissolution properties over time, risking damage to original surfaces. Solvent azeotropes are an alternative for maintaining consistent composition throughout evaporation while benefiting from high vapor pressure relative to pure solvents. In this work, we created learning experiences focused on studying the azeotropes of isopropanol:n-hexane and 2-butanone:cyclohexane mixtures. Both binary systems form homogeneous azeotropes and have been studied for their application in art conservation science. The evaporation behavior of these azeotropic systems was followed at room temperature via vapor pressure measurements, gravimetric analysis, and gas chromatography. When widely reported boiling point azeotropic compositions were used, these systems failed to maintain constant composition when evaporating at room temperature. Therefore, the azeotropic composition was theoretically calculated and empirically measured to determine the extent of the compositional change from the boiling point to room temperature conditions. The learning experiences are supported by conservative science work completed at the Indianapolis Museum of Art. Examples of the laboratory procedures, data, and results will be presented and discussed in light of their design and implementation for the General Chemistry laboratory program at Sam Houston State University.

Design of laboratory experiences in art conservation science: A study of the evaporation behavior of homogeneous azeotropes used to clean paintings at room temperature

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