| Summary: | Abstract The Morgan Library & Museum, New York, owns twenty-five works on paper by the 18th-century English artist Thomas Gainsborough. Scholarly publications over the past 20 years, as well as Gainsborough’s own writings, have highlighted his proclivity toward innovative methods and experimentation. In particular, a letter that the artist wrote in 1773 reveals details of his secret recipe for making oils on paper, such as his recommended use of lead white and the unorthodox practice of dipping his works in skim milk, possibly to prevent the pigments from discoloring. About a dozen of Gainsborough’s creations were included in a 2018 exhibition at The Morgan entitled Thomas Gainsborough: Experiments in Drawing. On this occasion, an in-depth scientific study aimed to explore the artist’s work as a draftsman, with a special focus on his mastery of materials, his technical innovations, and his development of an original approach to drawing. Initially, a selection of artworks was examined using magnification along with transmitted and raking light to improve surface visualization and to investigate the structure of each piece. Further photographic documentation with ultraviolet and infrared light was performed to gather preliminary information on the variety of white pigments employed, on the wet and dry chalk techniques used in certain works, as well as on the possible presence of coatings and underdrawings. Subsequently, scientific analysis by means of X-ray fluorescence (XRF) and Raman spectroscopies aimed at characterizing the white pigments present in The Morgan’s drawings, which mostly consisted of calcite and lead white. Moreover, a combination of advanced micro-sampling tools, i.e. polyvinyl chloride (PVC)-free erasers and fine polishing films, ad-hoc sample preparation methods, highly sensitive proteomics analysis via nano-liquid chromatography/mass spectrometry (nano-LC/MS), and sophisticated bioinformatics data processing was employed to assess Gainsborough’s use of skim milk as a “secret fixative” on some of his works. Results have revealed the presence of specifically bovine milk in all of the samples evaluated to date. Notably, only through the combined use of such advanced technical resources can the interrogation of all milk proteins retrieved from the samples provide evidence for the presence of a milk fixative and open the discussion about milk processing methods in the 18th century. In addition to granting conservators and art historians a deeper understanding of the complexity of Gainsborough’s drawing techniques, this study paves the way for further investigations to probe the use of casein-based fixatives by other artists working on paper such as Degas and Van Gogh.
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