Non-invasive analysis of Van Gogh’s drawing inks

To clarify his working practice, brown and purple inks on 42 drawings, executed by Van Gogh during the period 1878–1890, were identified by applying a non-invasive, portable technique: Fibre-Optics Reflectance Spectrophotometry (FORS). While the shapes of the spectral reflectance curves of the brown inks on the drawings closely matched those of applications on paper of iron gall and chrome logwood ink, the spectral reflectance curve of a purple ink on the drawing Montmajour (1888) matched that of crystal violet and of the ink on a contemporary letter written by Van Gogh. HPLC-analysis of the ink extracted from a paper sample, taken from the drawings’ edge, indeed showed this to contain crystal violet, in admixture with its de-methylated derivatives. XRF-analysis of the brown metal-containing inks confirmed the results obtained by FORS. These results indicate that, during his stay in Antwerp (1885), Van Gogh changed from iron gall to chrome logwood ink.