The role of agar gel in treating water stains on acrylic paintings: Case study of Composition, 1963 by Justin Knowles

This paper describes the historic context and explains the treatment rationale for minimizing disfiguring water stains on a large-scale, acrylic dispersion canvas painting: Composition, 1963, by British artist Justin Knowles. Composition is a brightly colored, hard-line geometric abstraction juxtaposed against an unpigmented acrylic dispersion-sized linen canvas. Accidental water damage produced tidal stains across the sized canvas, rendering it unexhibitable. Investigations into the relationship between materials and meaning in Knowles’ work, alongside literature on the cleaning of acrylic dispersion paintings, textiles, and works on paper facilitated the development of a tailored cleaning treatment involving the use of agar gel as an aqueous delivery system, which minimized risk to the painting materials, whilst facilitating a satisfactory reduction and subsequent visual integration of the water stain. As a final stage, a number of retouching media commonly used on acrylic paints were evaluated, and a successful method was determined using Aquazol 50 and dry pigments. The success of retouching was also evaluated via visual assessment, highlight-based RTI, and digital microscopy (HIROX). As a result of this collaborative approach, this important work has been successfully returned to displayable condition.