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.
In conservation, adhesives are commonly used for the consolidation of canvases, yet their impact upon the canvas longevity has raised some concerns amongst conservators. As such, this study presents a testing protocol developed to assess the performance of commonly-used adhesives (natural animal glue and synthetic Beva ® 371) and a newly developed nanocellulose consolidant, nanofibrillated nanocellulose (CNF). This includes their effect on the visual appearance, consolidation, and response of the mechanical properties of the treated canvases to programmed changes in relative humidity (RH). Scanning electron microscopy (SEM) images of animal glue-and Beva ® 371-treated canvases revealed the presence of adhesive and consolidant on and in-between cotton fibres. The consolidants form bridges linking and connecting the cotton fibres and holding them together, whereas the CNF treatment, formed a visible continuous and dense surface coating. None of the treatments induced any discernible colour change. Controlled environment mechanical testing was performed in two ways: by applying a linearly increasing static force at fixed RH (Young's modulus) and by applying a dynamic force together with a programmed RH cycling between 20 and 80% (RH dependent viscoelastic properties). CNF gave a higher value of Young's modulus than either of the two commonly-used materials. Measurements at different values of RH (20 and 80%) demonstrated for all the treated canvases that at the lower value (RH 20%) Young's modulus values were higher than at the higher value (RH 80%). Besides, the dynamic mode showed that the rate of response in all cases was rapid and reversible and that the nanofibrillated cellulose treated sample showed the highest variation in storage (or elastic) modulus measured at the end of RH plateaux (20 and 80% RH). Thus CNF appears to be a promising material given its higher mechanical performance. The protocol developed in this study has enabled us to examine and compare candidate materials for the consolidation of canvases systematically, using testing parameters that remained relevant to the field of canvas conservation.
During conservation treatment, consolidants and deacidifying agents can be added to the canvas of a painting to mechanically stabilise it and counteract the acidity that promotes degradation. In this study, new stabilising consolidants and deacidifying agents based on different nanoparticles (silica, calcium carbonate, magnesium oxide, cellulose nanofibrils and cellulose nanocrystals) were tested in comparison to traditionally used products. These products were applied onto different types of canvasses, and colour, gloss and pH changes were analysed. Conservators' subjective perceptions on the ease of application and the final visual results of the products were also assessed. Specifically, conservators were asked to examine the drying time and the ease of use of the products, as well as any changes in stiffness, darkening or whitening caused by the products on the canvasses. The best products were the ones based on calcium carbonate, magnesium oxide and cellulose nanocrystals. Cellulose nanofibrils are also promising consolidants because they are highly compatible with the chemical nature of painting canvasses.
A partir de datos inéditos obtenidos del estudio del sistema constructivo del soporte de madera se confirma que el frontal de san Cristóbal y los laterales de altar de Toses, actualmente expuestos separadamente y custodiados por el Museu Nacional d’Art de Catalunya (MNAC), forman un conjunto que originalmente guarnecía el altar principal de la iglesia de San Cristóbal de Toses (Ripollés, Cataluña). Estas obras, a pesar de su misma procedencia, han generado históricamente disparidad de opiniones acerca de la posibilidad de haber formado un único conjunto en origen, debido a la diferencia evidente de la calidad de la iconografía representada. Se trata de un hallazgo especialmente relevante dado que es el primer y único conjunto de frontal y laterales de altar del gótico lineal catalán conservado en la actualidad.
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