|
|
|
Acrylic medium: We are exploring the aging of acrylic dispersions by monitoring the changes in the chemical and physical properties of the film. The initial study focused on Liquitex acrylic gloss medium, an unpigmented polymer dispersion commonly used as a coating or diluent for acrylic paints. Films of Liquitex media dry to the touch very quickly, but they continue to cure over the next several months, developing their ultimate strength properties and also becoming less sensitive to solvents.1 The fully developed films are strong, elastic, and partially soluble (about 10%) in many mildly polar solvents. Light aging tests show the polymer to be extremely resistant to photochemical deterioration, typical of these types of acrylic polymers. Despite this chemical and physical stability these films experience two rapid appearance changes: they become slightly yellow and translucent.2 The haze that develops results from the crystallization of surfactants in the film, and the discoloration also seems related to the water-soluble additive materials in the product. Current work is focused on the origin, prevention, and bleaching of the yellow discoloration. Bleaching studies have been performed on the yellow discoloration of acrylic dispersion films typically used as artists' medium.3 Films, found to yellow during dark storage, were exposed to high levels of visible light typical of a light bleaching treatment. The exposure to light was effective at removing about 60% of the discoloration within the acrylic films. Subsequently storing the bleached films under moderate lighting (150 lux for 10 hours each day), which mimics typical museum conditions, prevented further discoloring of the acrylic films. Further, studies were performed to determine the efficacy of preventing the yellow discoloration before it can develop by exposing the films to the simulated gallery lighting. The moderate lighting condition was effective at either preventing or slowing the rate of yellowing of the acrylic films for many of the products tested.4 Acrylic gesso: Canvas is often coated with a primer to protect it from chemical reactions with paint layers, to enhance the adhesion of subsequent paint layers, and to provide a white or toned painting surface. Typically, acrylic gesso grounds are the material of choice used by either manufacturers of ready-to-use canvases or artists who prepare their own canvases. In our previous studies of acrylic medium,3 it was found that matter extracted from canvas into the medium can have a significant contribution to discoloration observed in acrylic dispersion media on canvas. Also during cleaning of paintings, there is a potential for water to penetrate through the paint layers and into the gesso or deeper where there is a potential of leaching material to the surface. We are measuring the water permeability of gesso films as a function of thickness and age as well as examining the quality of different products. The permeability of the film measures the gesso's barrier protection properties to prevent leaching of potential discoloring agents from a support. Also important is tracking the permeability of the gesso after multiple washings. Further, this project will focus on monitoring the films under normal and accelerated aging conditions while probing for changes in cohesion, adhesion, color, and surface roughness. For more information: |
The
future of modern acrylic paintings is difficult to predict due to the lack of
information on long-term polymer stability.