Nanocellulose has been recently proposed as a novel consolidant for historical papers. Its use for painting canvas consolidation, however, remains unexplored. Here, we show for the first time how different nanocelluloses, namely mechanically isolated cellulose nanofibrils (CNF), carboxymethylated cellulose nanofibrils (CCNF) and cellulose nanocrystals (CNC), act as a bio-based alternative to synthetic resins and other conventional canvas consolidants. Importantly, we demonstrate that compared to some traditional consolidants, all tested nanocelluloses provided reinforcement in the adequate elongation regime. CCNF showed the best consolidation per added weight; however, it had to be handled at very low solids content compared to other nanocelluloses, exposing canvases to larger water volumes. CNC reinforced the least per added weight but could be used in more concentrated suspensions, giving the strongest consolidation after an equivalent number of coatings. CNF performed between CNC and CCNF. All nanocelluloses showed better consolidation than lining with synthetic adhesive (Beva 371) and linen canvas in the elongation region of interest.

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.

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The aim of this work was to evaluate the use of novel nanocellulose-based consolidants for modern easel paintings as a possible alternative to lining and to the use of common adhesives. Two dispersions of consolidants were tested: nanofibrillated (CNF) and nanocrystalline cellulose (CNC). A model cotton canvas was used to evaluate the effect of these consolidants following treatment by the nanocellulose-based formulations. The surface appearance of the canvases was assessed before and after treatment using colorimetry and scanning electron microscopy (SEM). Additionally, the characterisation of the mechanical properties of the samples was performed using tensile testing and dynamic mechanical analysis (DMA-RH) at controlled relative humidity (RH) (3 RH cycles, 20-60-20% RH at 25 °C) before and after treatment. Finally, colour changes undergone by the samples upon accelerated ageing were measured by colorimetry. Taking into account the individual outcomes of each of these tests, it was possible to evaluate the merits and limitations of the use of nanocellulose treatments for the consolidation of modern painting canvases.

We surveyed the canvas of 31 paintings from the collection of the Museu Nacional d'Art de Catalunya, Barcelona, Spain, using non-destructive near infrared spectroscopy (NIR) in order to determine the pH and degree of polymerisation (DP) of the canvas supports. The data showed that the canvases, all from 1890 to 1910, are acidic (average pH 5.1 ± 0.4) and fairly degraded (DP 710 ± 260). Using the doseresponse function for cellulosic materials with pH, DP, T, and relative humidity (RH) as inputs, the rate of degradation can be calculated, as well as the period of time until the point when the canvases become so fragile that their handling could lead to mechanical damage and thus risk the integrity of paint layers. On the basis of the survey data, we calculated isochrone plots as well as demographic curves for the collection. Using these, we explored a number of conservation management scenarios and compared them with the expected rate of degradation under current average environmental conditions (21°C, 58% RH). At these conditions, it is predicted that the average canvas will become fragile and might require interventive treatment in ca. 140 years. However, if the storage temperature is decreased, or if the canvases are deacidified, the period of time until treatment becomes necessary can be considerably increased. As a separate case study we also present a survey of the canvas of The Woman in Hat and Fur Collar (Marie-Thérèse Walter) by Pablo Picasso. The pH and DP of this canvas was determined in 15 sampling points, the averages being pH 5.6 ± 0.2 and DP 1700 ± 320, which allowed us to calculate the isochrone plot for this canvas.