Acrylic paintings

By Bettina Ebert, Paintings Conservator and Researcher, Asiarta Foundation

Acrylic paints were introduced in the 1950s, and artists soon enthusiastically embraced this alternative painting medium. Their handling properties allow artists great freedom – their fast drying time and the ability to thin with water instead of solvents when compared to oil paint are favoured by many artists.

A contemporary acrylic painting by Nguyễn Văn Cường

Acrylic emulsion paint has a complex formulation, generally consisting of pigments, extenders, wetting agents, dispersing agents, thickeners or rheology modifiers, emulsifiers, buffers, de-foamers, freeze/thaw stabilizers, preservatives and coalescing agents in an acrylic polymer dispersion. Acrylic paints are very stable and resistant to deterioration, especially when compared to other paint systems.

Acrylic emulsion paint dries by evaporation of water. As water is lost from the system, polymer particles are brought into contact. Further evaporation of water leads to the deformation and coalescence of particles into an ordered polyhedral array. The result is a dried and continuous polymer coating. An acrylic emulsion goes from about 40% solids content to 100% solids on drying, leading to a great reduction in surface area.

Acrylic paints are thermoplastic. Their low glass transition temperature means that they are very soft and flexible at room temperature. While this reduces the formation of cracks, it brings with it inherent dangers. A tacky surface will imbibe dirt which may be very difficult to remove afterwards. During transport and storage, packing materials may stick to the paint surface. Acrylic paint films respond to low temperatures and low relative humidity by becoming brittle, making them prone to cracking. A dried acrylic paint film contains micro-voids, making the film porous. This brings with it benefits as well as disadvantages, since a porous coating may imbibe dirt and pollutants. During the cleaning process, these voids may trap components of the cleaning formulation. Since acrylics are non-conducting, acrylic paint surfaces may build up static charge, attracting dirt particles from the environment.

Acrylics are sensitive to water and polar solvents, raising cleaning issues. Aqueous cleaning systems readily remove surfactant from the paint surface and cause swelling of the paint film, although the paint remains generally stable. Surfactants are added as initiators to the polymerization process. In addition, surfactants are included in the paint formulation as dispersants, wetting and coalescing agents. Whether the removal of surfactants during cleaning adversely affects the paint is yet to be researched. Cleaning may have an effect on the surface appearance – uneven gloss or tidelines may result. Non-polar organic solvents such as white spirit do not appear to affect acrylic paint. However, acrylics are very sensitive to organic solvents such as alcohols and ketones.

Since conservation research into acrylic paint is still in its early days, emphasis on preventive conservation of acrylic paintings must be stressed. Correct handling, storage and display of acrylic paintings will reduce the need for cleaning or other interventive conservation treatment. Framing and/or glazing the painting will provide protection from accidents and eases handling and transport. Environmental control that avoids extremes of temperature and humidity is beneficial due to the thermoplasticity of acrylics as described previously. When handling an unframed acrylic painting, gloves should be worn as fingerprints on the acrylic paint surface preferentially attract dirt and can become almost impossible to remove over time. Packing materials should not come into contact with the paint, as they may stick to the surface. Plasticisers are present in bubble wrap and, if this is allowed to touch the paint film, it may leave circular marks on the paint surface.

Painting conservation is a specialist field requiring extensive knowledge. Here is a brief summary of the different techniques available to painting conservators.

More information about the artist Nguyễn Văn Cường, whose work is featured in this article, is available through Witness Collection.

The following articles provide more information on conservation of oil paintings, lacquer paintings and paper.