Retouching unvarnished acrylic emulsion paintings, a comparative study

Acrylic films have specific characteristics such as sensibility to polar organic solvents (and in some extent water) and are prone to accidental superficial alterations. Most of the necessary retouching caused by accidental alterations is directly on the film so the notion of reversibility is crucial. This is why this study is focused on retouching media that are already proven to be suitable for acrylic paintings. Those materials are then soluble in either water or aliphatic hydrocarbons. The tested materials are Aquazol® 200 and 500, Klucel® G, gum Arabic, and Regalrez® 1094 mixed with pigments. Ready to use materials (Aquacryl®, QOR®, and Winsor & Newton® watercolours) were also tested. Various criteria were examined: first, all the materials were tested unpigmented and mixed with titanium white. Then, their gloss and colour change were measured, to see which material is more prone to produce matte films. A set of samples were then exposed to artificial light aging, and another set exposed to high relative humidity in order to isolate the impact of light and humidity on the gloss and colour of the resins (like yellowing) and observe how the retouching could behave in poor conservation conditions. Empirical tests were also conducted: the resins were mixed with five different pigments to see difference in opacity and saturation between materials. Most importantly, the materials were tested on naturally aged acrylic paintings, to see which material(s) are easier to use. The aim of this study was not to find the best retouching material, but rather to validate and enlarge the possibilities for the retouching of acrylic painting.