The secret recipes of Thomas Gainsborough
Minimally invasive proteomics analysis reveals the recipe that Gainsborough kept secret for his whole life.
About the project
The project is a collaboration between the Morgan Library&Museum, Network Initiative for Conservation Science (NICS), the Department of Scientific Research of the Metropolitan of Art (New York, USA), and the University of Bordeaux (France). An in-depth scientific study of eleven of Gainsborough’s works housed at The Morgan Library & Museum has been performed to get an insight into the artist’s mastery of materials and innovative drawing techniques.
Self portrait of Thomas Gainsborough, 1759.
The artist
Thomas Gainsborough (1727–1788) is a central figure in 18th-century art. Highly renowned for his portraits and landscape paintings, the artist also produced over 900 drawings, experimenting with various media on paper, such as graphite, chalk, oil, watercolours, pastel, and protein-based compounds to obtain original visual effects. The artist accomplished “experiments on paper”, disrupting traditional drawing rules and creating new visual effects by improving original styles.
The innovative technique
Gainsborough’s described his unique recipe for “oils on paper” in a letter written in January 1773 to his friend William Jackson (currently stored at the Yale Center for British Art). The document reported the application of lead white pigment on the paper surface and the subsequent dipping of the entire drawing in skim milk multiple times to enhance the attachment of pigments and potentially to possibly prevent their discolouring. The wet drawing was adhered to a temporary wooden frame or stretcher lined with paper. Auxiliary light and dark layers were added, followed by a second dipping in milk. Colours were then applied together with an Arabic Gum glazing. The final steps reported in the letter werethe application of three varnish layers (natural resin) on both sides (to keep the paper flat) and removing the drawing from the strainer and its mounting. The recipe reported in the letter remained a secret for a long time by the will of the artist himself: “Swear now never to impart my secret to anyone living”.
Minimally invasive sampling was performed using microgrits and PVC erasers.
The multidisciplinary approach
Imaging Techniques
The drawings were investigated with transmitted and raking light to provide information about the paper surface’s internal structure and texture, respectively. Magnification at visible light was implemented to study the media and reveal the potential presence of underdrawings. Then, the drawings were examined with ultraviolet (UV) and infrared (IR) radiation to gain insight into Gainsborough’s working methods. This examination mainly aimed to document the use of opaque lead white, the application of overall and selective coatings (natural resins) or fixatives, and the presence of black chalk underdrawings (no resin coatings were identified). Gainsborough’s practice of dipping his drawings in a fixative bath of milk was supported by the observation of a clean corner at the upper left of “Landscape with Horse and Cart Descending a Hill” (ca. 1780; III, 63), that possibly corresponds to the location where the work might have been held by the artist while dipping it in milk.
XRF and Raman Spectroscopy
Non-invasive X-ray fluorescence (elemental analyses) and micro-invasive Raman spectroscopies revealed the application of different white pigments (lead white and calcite).
Mass spectrometric based proteomics
Bottom-up and top-down proteomic strategies were performed on micro samples (minimally invasive sampling with PVC-free erasers and microgrit polishing paper) using high-resolution mass spectrometry (nanoLC-ESI-MS/MS). The detection and characterisation of numerous milk proteins specific to Bos taurus (domesticated cattle) revealed the application of milk-based fixatives in the analysed Gainsbororugh’s drawings. The information achieved with the proteomic analysis, such as the specific speciesfrom which the detected proteins originate, and their modifications (mainly related to ageing), was enriched through top-down analysis that highlighted highly modified proteoforms characterised by multiple cleavage patterns.
MS/MS spectra for milk proteins that were detected on one of Gainsborough’s drawings. On the left, a peptide belonging to the kappa-casein protein, and on the right, a peptide belonging to the lactadherin protein. Modifications typical of age-related degradation are detected in the first spectra, with the oxidation of tryptophan (W) and deamidaiton of asparagine (N).
The impact
The study has given a deeper understanding of the complexity of Gainsborough’s materials and innovative drawing techniques, providing the first analytical proof that the artist used a milk-based fixative. The proteomic study implemented minimally invasive sampling methods (polyvinyl chloride (PVC)-free erasers and fine polishing films) allowing safe sampling of the drawings with minimal optical impact
Future perspective
Further investigation of the presence of polysaccharides and natural resins may give a better insight into Gainsborough’s technique and potentially help in better understanding the yellowing in the drawings, which remains unclear. However, sampling is still a barrier to these studies. Furthermore, while Gainsborough described the application of skim milk, some milk fat remained in his 18th-century processed milk. The characterization of 18th century skim milk also prompts further studies. The study has also prompted further investigations of the protective action of milk on lead white from pollution and subsequent conversion to lead sulphide. It also adds strength to the argument to probe for the use of casein-based fixatives by Gainsborough’s contemporaries working on paper such as Degas and Van Gogh.
Related Publications
Pozzi, F., Arslanoglu, J., Galluzzi, F., Tokarski, C. and Snyder, R., 2020. Mixing, dipping, and fixing: the experimental drawing techniques of Thomas Gainsborough. Heritage Science, 8(1), pp.1-14.
Research performed in collaboration with…
This project has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement No.722606