Varnishing as part of the conservation treatment of easel paintings

Projeto interdisciplinar de estudo e conservação da série “Retirantes” de Candido Portinari no Museu de Arte de São Paulo

“…Uma camada de Regalrez® 1094 a 40% em aguarrás mineral foi aplicada com trincha sobre toda a superfície pictórica de forma a proteger a pintura. O Regalrez® foi escolhido por ser uma resina sintética de baixo peso molecular, muito estável no tempo, resistente à oxidação e, sobretudo, bastante reversível, pois permanece solúvel em solventes pouco polares (De la Rie e McGlinchey 1990;McGlinchey 1990;Leonard 1990, Whitten 1995De la Rie 2003, Mariotti e Borgioli 2004Von der Goltz et al 2012), permitindo uma limpeza muito fácil, o que evitará tratamentos futuros que possam sensibilizar novamente os pigmentos originais.…”

A Formulation for a New Environmentally Friendly Varnish for Paintings

“…An ideal varnish should remain colourless, transparent, removable over time, and should have the correct mechanical properties of strength and flexibility to follow any movement of the underlying substrate without cracking. In addition, the varnish composition should be known and carefully evaluated towards its proper application as it should not alter the integrity of the paint film [1,4,6]. Varnishes for paintings are generally organic-solvent-based, and the formulations are made by solubilising the resin in a low polarity solvent mixture with the highest dispersion factor (f d ), related to the percentage of dispersion forces as defined by the Teas solubility concept, to reduce any interactions with the binder or other pictorial materials [7][8][9][10][11][12][13].…”

“…Materials originally used as painting varnishes (typically natural resins) can alter at the molecular level mainly due to photo-oxidative degradation, resulting in loss of transparency, yellowing, and change of solubility. For this reason, varnishes are replaced over time during art restoration work, and over the years research has sought to find more stable products [1,4,6]. In the 1920s, synthetic polymer resins, generally considered more stable than natural resins, were introduced to the market.…”

“…In the 1920s, synthetic polymer resins, generally considered more stable than natural resins, were introduced to the market. However, varnishes obtained with synthetic polymers often give paints a different appearance from those produced with natural resins [6,9,14]. Starting from the 1980s, studies conducted primarily by de la Rie to identify potential substitutes for natural resins [8,[14][15][16] have shown that low molecular weight (LMW) synthetic resins can produce films with an appearance similar to those with natural resins and have better stability.…”

“…Nowadays, LMW resins of the hydrogenated hydrocarbon type (e.g., Regalrez ® 1094) and the urea-aldehyde type (e.g., Laropal ® A81) are widely used in art restoration. These are, respectively, soluble in mixtures without or with a limited content of aromatic solvents [1,6,8,17]. Considering the adverse effects on paint films attributable to aromatic solvents (limiting swelling, solubilisation, and leaching) and the growing concern about the toxicity-related impacts on the environment and humans, the ability to use low polarity solvents potentially less damaging to conservators and paintings is a significant feature [1,8].…”