Systematic mechanical assessment of consolidants for canvas reinforcement under controlled environment.

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

Nanomaterials for the cleaning and pH adjustment of vegetable tanned leather

Leather artifacts in historical collections and archives are often contaminated by physical changes such as soiling, which alter their appearance and readability, and by chemical changes which occur on ageing and give rise to excessive proportion of acids that promote hydrolysis of collagen, eventually leading to gelatinization and loss of mechanical properties. However, both cleaning and pH adjustment of vegetable tanned leather pose a great challenge for conservators, owing to the sensitivity of these materials to the action of solvents, especially water-based formulations and alkaline chemicals. In this study the cleaning of historical leather samples was optimized by confining an oil-in-water (o/w) nanostructured fluid in a highly retentive chemical hydrogel, which allows the controlled release of the cleaning fluid on sensitive surfaces. The chemical gel exhibits optimal viscoelasticity, which facilitates its removal after the application without leaving residues on the object. Nanoparticles of calcium hydroxide and lactate, dispersed in 2-propanol, were used to adjust the pH up to the natural value of leather, preventing too high alkalinity which causes swelling of fibers and denaturation of the collagen. The treated samples were characterized using Scanning Electron Microscopy (FE SEM), controlled environment dynamic mechanical analysis (DMA-RH), and infrared spectroscopy (ATR-FTIR). The analytical assessment validated the use of tools derived from colloid and materials science for the preservation of collagen-based artifacts

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

A new analytical method was developed to non-destructively determine pH and degree of polymerisation (DP) of cellulose in fibres in 19th–20th 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

Compromised dental cells viability following teeth-whitening exposure

This study aimed to assess the viability of dental cells following time-dependent carbamide peroxide teeth-whitening treatments using an in-vitro dentin perfusion assay model. 30 teeth were exposed to 5% or 16% CP gel (4 h daily) for 2-weeks. The enamel organic content was measured with thermogravimetry. The time-dependent viability of human dental pulp stem cells (HDPSCs) and gingival fibroblast cells (HGFCs) following either indirect exposure to 3 commercially available concentrations of CP gel using an in-vitro dentin perfusion assay or direct exposure to 5% H2O2 were investigated by evaluating change in cell morphology and by hemocytometry. The 5% and 16% CP produced a significantly lower (p < 0.001) enamel protein content (by weight) when compared to the control. The organic content in enamel varied accordingly to the CP treatment: for the 16% and 5% CP treatment groups, a variation of 4.0% and 5.4%, respectively, was observed with no significant difference. The cell viability of HDPSCs decreased exponentially over time for all groups. Within the limitation of this in-vitro study, we conclude that even low concentrations of H2O2 and CP result in a deleterious change in enamel protein content and compromise the viability of HGFCs and HDPSCs. These effects should be observed in-vivo

On the potential of using Nanocellulose for consolidation of painting canvases

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