A chemical study of organic materials in three murals by Keith Haring: A comparison of painting techniques

The paint materials in three different Keith Haring outdoormurals, Tuttomondo in Pisa (1989), the Necker Hospital mural in Paris (1987), and the Melbourne mural (1984), were investigated using pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS). The aim of the study was to characterize the chemical composition of the paint materials used by the artist in the three mural paintings and to correlate their chemical composition to their state of conservation. The analyses were performed using a PY-3030D pyrolyzer (Frontier Lab, Japan). The analyses of the paint samples from Tuttomondo showed the presence of a styrene/n-butylacrylate copolymer, which had been used as a paint binder. The results were then compared with those obtained with a Pyroprobe 5000 pyrolyzer (CDS Analytical, U.S.A.). The pyrolysis profiles of the paint samples of the Paris muralwere characterized by the presence of benzene and acetic acid, together with small amounts of toluene, styrene, indene, and different aromatic compounds, which indicated the presence of a vinyl resin. The various isomers of the vinyl ester of versatic acid were attributed to VeoVaTM, present in the vinyl polymer as an internal plasticizer. In the Melbourne mural, there was a high heterogeneity of paint materials, both original and deriving from a restoration intervention. The Py-GC/MS analyses revealed the presence of alkyd, vinyl, and acrylic resins. The samples were collected within the framework of conservation campaigns carried out on the three artworks. The results enabled the materials used by the artist to be identified, and highlighted the conservation state of the murals. They also provided conservators and restorers with helpful information for the choice of cleaning and protection procedures. Having access to three different examples of Haring's street art enabled us to compare the paint techniques and to relate them to the state of conservation.