While some research has been devoted to studies of the paint layer, it is the canvas that provides crucial mechanical support to it. This topic is of utmost interest to painting conservators and is particularly of concern to contemporary canvases because these are still ‘treatable’, while older canvases are usually lined, or so degraded that any stabilization treatment would only have a limited effect. It is fundamental to stress that the degradation of canvas affects greatly the stability of the paint layer. Recent collaboration between UB and UCL [M. Oriola, A. Možir, P. Garside, G. Campo, A. Nualart-Torroja, I. Civil, M. Odlyha, M. Cassar, M. Strlic, Anal. Meth., 2014, 6, 86-96] has shown that acidity of canvases made of natural materials is generally of concern as it can lead to loss of mechanical properties and deterioration of canvases based on natural materials in less than 100 years (in line with our knowledge of cellulosic materials), which then requires costly conservation interventions, inevitably affecting the paint layer as well. The stability of synthetic canvases is even less known than that of canvases of natural origin and in need of research. This problem dramatically concerns also jute, which becomes quite acidic in a faster way than linen, and paintings done on this type of canvas become more brittle. Some paintings done on jute, already identified, are available at MNAC (Barcelona), and at the Art Collection of the Faculty of Fine Arts (UB). There are many important paintings on jute such as Picasso’s Guernica at Reina Sofia in Madrid (linen and jute), or paintings by Van Gogh, Gauguin, and the German expressionists (Kirchner, Müler) affected by this problem, so there is a significant potential for impact of this research.
The goal within NANORESTART was to develop materials for the mechanical strengthening of canvases of modern/contemporary paintings, which was addressed by WP3.
Another challenge related to the stabilization of modern/contemporary artifacts involves the consolidation of painted layers and plastic surfaces. Due to aging, original additives such as surfactants and plasticizers can migrate from the bulk to the surface of these artifacts and form exudates. These additives can then be lost as a result of aging or even surface cleaning interventions, since most acrylic paintings are unvarnished [B. Ormsby, T. Learner, Reviews in Conservation, 2009, 10, 29-41]. The loss of plasticizers can result in brittleness of the painted layer, requiring stabilization to avoid cracks. However, the presence of plasticizer exudates on the surface of artifacts favors dirt pick up. Therefore, the need of removing these compounds and replacing them with new plasticizers (only when deemed necessary) is still debated and must be carefully evaluated case by case.
Cracking of acrylics (including also acrylic/styrene and acrylic/vinyl acetate) can also be due to the use of unsuitable painting techniques or exposure to cold temperatures. Alkyd colours are very sensitive to UV, water and heat, and often exhibit brittleness. In addition, modern oil paint films are beginning to pose similar challenges due to inherent water and solvent sensitivity. Some of the chemical and physical causes of water sensitivity have been already investigated, however solutions for conservation treatment remain elusive. Even in these cases, the addition of plasticizers to stabilize brittle painted layers must be carefully evaluated to avoid drawbacks as explained above.
The consolidation of painted layers and plastic surfaces was addressed as a secondary task (“seed task”), described in WP3.