Looking beneath Dalí's paint: non-destructive canvas analysis

Abstract

A new analytical method was developed to non-destructively determine pH and degree of polymerisation (DP) of cellulose in fibres in 19 th -20 th century painting canvases, and to identify the fibre type: cotton, linen, hemp, ramie or jute. The method is based on NIR spectroscopy and multivariate data analysis, while for calibration and validation a reference collection of 199 historical canvas samples was used. The reference collection was analysed destructively using microscopy and chemical analytical methods.Partial least squares regression was used to build quantitative methods to determine pH and DP, and linear discriminant analysis was used to determine the fibre type. To interpret the obtained chemical information, an expert assessment panel developed a categorisation system to discriminate between canvases that may not be fit to withstand excessive mechanical stress, e.g. transportation. The limiting DP for this category was found to be 600. With the new method and categorisation system, canvases of 12 Dalí paintings from the Fundació Gala-Salvador Dalí (Figueres, Spain) were non-destructively analysed for pH, DP and fibre type, and their fitness determined, which informs conservation recommendations. The study demonstrates that collection-wide canvas condition surveys can be performed efficiently and non-destructively, which could significantly improve collection management.

Collections care scenario appraisal for painting canvases at Museu Nacional d'Art de Catalunya, Barcelona, Spain

“…It is therefore safe to assume that environmental pollution is not going to represent a major source of acidification in the near future. Local staining and discolouration does not seem to result in significantly higher local acidity either (Oriola et al, 2014), which would mean that future acidification is likely going to be a consequence of natural degradation processes inherent to canvas. It is of interest to compare MNAC averages with the data obtained from the survey of 12 Dalí paintings from Teatre-Museu Dalí, Figueres, Spain (Oriola et al, 2014).…”

“…Several measurements were made per canvas, typically up to 7, and the average is reported. Using the canvas identification algorithm based on linear discriminant analysis of NIR spectra (Oriola et al, 2014), bast, cotton, and jute fibres were identified, however, out of the 31 surveyed paintings, only 3 were made of jute and 3 were made of cotton fibres, the rest were all made of bast fibres.…”

“…Using the previously developed methodology based on NIR spectroscopy of painting canvases (Oriola et al, 2011(Oriola et al, , 2014, pH and DP were determined for 31 canvas paintings by Catalan painters, from 1890 to 1910, at the Museu Nacional d'Art de Catalunya, Barcelona, Spain (MNAC) (Supplementary material 1). A painting by Pablo Picasso from 1937 was also analysed using this technique.…”

“…The NIR method for determination of pH and DP of historic canvases as developed in previous research (Oriola et al, 2014) was used in the survey (errors of prediction being ±0.4 for pH and ±270 for DP determination). The spectra (100 averaged spectra per measurement spot) were taken at the back of a painting using a LabSpec 5000 NIR spectrometer equipped with fibre optics and a custom-made attachment for spectral collection in the 45°/45°geometry.…”

“…NIR spectroscopy was first used to survey a collection of painting canvases non-destructively in the Teatre-Museu Dalí in Figueres, Spain (Oriola et al, 2014). The DP and acidity of 12 canvases were determined using this technique, based on the same principle as previously used for historic paper (Trafela et al, 2007), historic textiles (Richardson et al, 2008), photographs (Fenech et al, 2013), and other types of collections.…”