I had stepped into an artist’s shop in New Orleans. What had attracted me were the vibrant colors in his paintings. I had assumed that he must have used acrylic paints.
To confirm my suspicions I questioned the artist, “Are you using acrylics?”
He defensively replied, “What great artist has ever used acrylic paints?”
At the time, none came to mind. Acrylic paints, which were developed after World War II, do not have a long history. In the short time that these paints have been sold, however, some notable artists have used them for their major works. These include Thomas Hart Benton, Diego Rivera, Andy Warhol, Roy Lichtenstein, David Hockney, Robert Motherwell, Barnett Newman and Mark Rothko. To be clear, the New Orleans artist was not in the same league as the artists cited.
The Advantages of Acrylic Paints.
Many artists look down their noses at acrylic paints. You may be one of them. While you can’t blend colors as easily with acrylics as you can with oil paints, acrylic paints possess several advantages that oil paints don’t possess.
Oil paints can take days to cure. Acrylic paints, on the other hand, dry fast, so you can complete a painting much faster. If you need to slow down the drying, you can spray the surface with water. New acrylic paints are also available with longer open times.
Although many acrylic colors are overly bright or garish, you can purchase acrylic colors which are indistinguishable from oil colors. In fact, the infamous art forger John Myatt used acrylic and other emulsion paints to fake more than 200 artists, including Van Gogh, Matisse, Chagall and Picasso. His forgeries fooled Christie’s and other dealers and now hang on the walls of museums such as the Tate.
In addition, acrylic paints allow artists to paint on a variety of media, including synthetic paper, cloth, leather, wood, aluminum composite panels and canvas. Above all, acrylics are durable, as I will explain in this article. They are also much safer to use than oil paints.
Different Paint Chemistry.
Paint is primarily comprised of a resin or binder and pigment. From one type of paint to another the pigment is basically the same. What differentiates paint systems is the binder. Tempera uses egg yolk as a binder. Gouache, which is similar to watercolor, uses gum arabic for its resin. Oil paint uses a drying oil, such as linseed oil or walnut oil as its resin. Acrylic paints, on the other hand, use an acrylic polymer emulsion as its resin or binder.
Another difference is how the binder dries or cures. In oil painting, the oil resin oxidizes after the paint is applied. As it does, shorter molecules polymerize, forming longer molecular chains. After these longer polymer chains form, they crosslink, in which the chains attach to one another. As the crosslinking process continues over time, the paint film becomes more and more rigid and brittle. Under stress, the brittle film can crack, which is a very common characteristic of oil paintings.
In comparison, acrylic paints, which are water-based, are comprised of long molecular chains while the paint is still in the tube or jar. After the paint is applied to the substrate, it forms a film as the water in the paint evaporates. It undergoes very little crosslinking as the paint dries. Instead, as acrylic paint forms a softer and more flexible film, the individual molecular chains entangle and coalesce. While the acrylic film can harden over time, the aging process is much slower than it is with oil paints.
The durability of a film is in part affected by the crosslinking process over the life of the film. However, it can also occur, if the long polymer chains break apart. Several factors can affect this disintegration process. These include chemical reactions between the pigments and the resin, especially if the pigment is alkaline in nature; exposure to heat, humidity and ultraviolet light; and the effects of oxidation and air pollution.
Some conservators believe that acrylic paints are less susceptible to environmental stresses, if the painting is stored in a controlled environment, such as a museum. Exposure to long periods of high heat accelerates the aging process and should be avoided. Excessive cold, heat and humidity also affects the durability of oil paintings.
As a word of caution, however, you should never subject acrylics to ambient temperatures below 50°, while you are painting or for several days after painting, while the paint continues to dry. If acrylics are exposed to low temperature, the paint film may not properly form.
Accelerated weathering tests, in which acrylic paints have been exposed to ultraviolet light, extreme temperature and humidity, suggest that the acrylic polymer resin is much more durable than a drying oil. However, keep in mind, that while these tests can provide statistically reliable indication of how a product should perform, it cannot guarantee how a product will actually perform in the real world. Based on test results, acrylic paintings should survive many millennia in a museum environment.
Most artists are certainly aware that oil paints are prone to yellowing. Some drying oils can yellow more than others. In addition to oxidation worsening yellowing, exposure to some cleaning chemicals can exacerbate the problem. In comparison to drying oils, acrylic polymer resin is relatively clear.
What might be viewed as a disadvantage of acrylic paint is that it tends to attract dirt. As I had noted earlier, acrylics are much softer and more flexible than oil paint films. The large acrylic molecules are also more porous. While these features may provide acrylic films with greater durability, its surface more readily traps dirt.
You will remember that acrylics are susceptible to many chemicals including some cleaners. Varnishes may also be incompatible with the paint. One solution to preventing dirt from adhering to an acrylic painting is to protect the painting under museum glass. For those paintings not framed under glass, cleaning should consist of wiping the surface with a damp, lint-free rag. Remember that the porous surface of acrylic paint can not only trap dirt, but it can also trap any cleaning chemicals that you may use. These chemicals, especially those that are alkaline, can degrade the resin.
The chemistry of the pigment, as well as the properties of the additives and fillers, can affect the appearance, adhesion and durability of the dried film. Some of the additives that manufacturers add to acrylics are surfactants, which lower the surface tension of a liquid, helping the paint to wet out on the substrate. Over time, these surfactants can leach to the film’s surface, clouding the brilliance of the paint’s colors. Wiping the painting down with a clean, damp cloth will generally remove any surfactants without affecting the durability of the paint.
Proper substrate preparation is critical in ensuring good adhesion to the support. In prepping canvas for oil painting, coating the surface with rabbit skin glue and gesso is required. When painting with acrylics, you don’t need to gesso the surface. In fact, you don’t need to use canvas. Instead, aluminum composite panels, which you have scuffed with sandpaper or a Scotch-Brite™ pad and coated with a primer such as XIM UMA, should provide a much better support for your acrylic paintings.
Earlier I noted that the types of pigments used in either oil paints or acrylic paints are basically the same. While acrylic polymer resins promise remarkable longevity, lightfastness depends on the pigments used in the paint. For this reason, when selecting a tube of paint, only buy those colors with a lightfast rating of either I or II. This same recommendation also holds true when buying oil paints.
My final bit of advice is to buy from a reputable manufacturer. These companies include Golden Artist Colors, Inc., Lascaux Colours, Atelier, Liquitex Artist Materials, Inc. and Winsor & Newton.