|The Gravity of Light, 48" x 36", acrylic|
BRAD TEARE The acrylic paintings I’ve created over the last decades show no signs of fading or cracking. Is there any reason to believe the current robustness of the paint film will fail at some point in the future?
MARK GOLDEN Because of the need to communicate as clearly as possible let me start with the most accurate answer: there is no reason to believe that quality artist acrylic paints will fail in the near future or even the far future–as distant as 500 to 1000 years.
This is not to say that acrylics don’t have their own problems but acrylics are not going to suffer damage like other plastics such as nitrocellulose, PVC, or styrene. Nor will artist acrylics suffer to the same extent as artist oils–which have problems with embrittlement and yellowing.
We only have a 70 year history with artist acrylics so our timeline is relatively short. Yet when we compare artist acrylic paintings to similarly aged artist oils we can confidently say that acrylic films are holding up well and compare favorably to more established media.
BRAD I’ve read that acrylic paintings by Andy Warhol, David Hockney, and Mark Rothko are beginning to fail. Is there a reason for this? Should this be a cause for concern for those of us using acrylics?
MARK This is exactly where recent authors of various blogs and articles have both conflated issues and misled painters. One clear example was an article showing a conservator working on a Warhol painting with the text suggesting it was in disrepair. The photo actually illustrated a cleaning project and, in fact, the piece is in wonderful shape.
While it’s true that conservators and conservation scientists are working to develop the best ways to clean acrylics it is not the case that these paintings are failing. Most of Rothko’s work that failed were from the misuse of oil paint. Hockney started using acrylic in the 60’s and 70’s and it was an important media shift for the work he was doing at the time. Those acrylic paintings have been holding up very well.
BRAD I’ve had oil paintings crack from being struck as well as cracking when taken off the stretchers. I’ve had no similar problems with my acrylic paintings. Are there cases when an acrylic will crack?
MARK Acrylics create a wonderfully flexible film but there are unique situations that can cause acrylics to crack. Quite a bit of research has been conducted into the changes acrylics undergo in low temperatures. As we get to 52˚F and below acrylics get stiffer. Below freezing acrylics are as brittle as oil paintings and can crack if shocked, dropped, poked, or unrolled.
Finally, there can be a type of cracking called crazing during drying. If a film forms on the surface of a thick acrylic and the painting is moved before it has a chance to fully dry it is possible to tear the surface which then creates a craze in the film. Also if one adds too much water to the acrylic and works thickly with the product it is possible to create crazes in the film. And finally if one uses thin mediums and tries to pool them up into thicker films as the water evaporates it can create too much stress on the upper level of the film creating river valley-like crazes.
BRAD To my understanding the archival quality of paint has three factors–the lightfastness of the pigment, the visual stability of the medium, that is, whether the medium will cloud or acquire unwanted color over time, and structural stability–whether the medium will crack, flake, or suffer other structural problems. Do these concerns accurately describe potential archival problems?
MARK The main concern is this: will a medium fail and destroy the artists’ intent to the point the work is no longer meaningful except as a historical artifact? Such failure includes fading, darkening, or changing of pigments exposed to various conditions, light being the most damaging.
Other failures include the visual stability of the medium, clouding, yellowing, opacifying, or various exudates from the binder or additives (that is, the appearance of sticky, gooey, or crystalline substances). And finally structural stability of the paint medium and its components. Structural stability is a bit more complex and confusion often exists as to the current best practices regarding how to conserve acrylic paintings.
BRAD Anyone visiting a museum can see how some old oil paintings have cracked. Painting conservators observed these failures and formulated best practices to help avoid such problems. Since acrylic paints are such a new technology how do scientists test the paint to predict how acrylics will age over time? Are these tests reliable?
MARK That is a wonderful question to ask the conservation community as they survey work in their museums–How many oil paintings on canvas in your collection have cracked? You might find a great majority have. But typically the cracks will have been made less noticeable by multiple conservation treatments. We don’t impugn the reputation of such oil paintings because they’ve cracked. It is understood that this is a normal result of many of the conditions that oil paintings have faced over time.
But your question is really: how reliable is the testing since acrylic have only been around for only 70 years? The answer is there are several compelling studies. In an 1976 article by the USDA Forest Service they conclude that acrylic waterborne dispersions are more stable in outdoor conditions than oils or alkyds (read article here).
The USDA has other reports but the outdoor environment study is the most interesting as outdoor environments are the harshest. The more layman friendly article (read here) reports the same basic conclusions from the first article: Acrylic latex resins are flexible and very durable. A good acrylic latex outdoor house paint will generally outlast a good oil-based house paint, and again … acrylic polymers are more resistant to sunlight than oil-based paints and therefore do not weather as quickly.
There are also accelerated aging studies of exposure of acrylic dispersion polymer to artificial ultra violet light. In a study by Prof. Paul M. Whitmore and Dr. Val G. Colaluca, The Natural and Accelerated Aging of an Acrylic Artists’ Medium (Studies in Conservation 40(1): 51-64 January 1995) they review the mechanism of failure with UV exposure. Clearly, the ethyl acrylate polymer undergoes chain scission under UVB exposure. This leads to a breakdown of tensile strength, chalking, and severe failure of the film. They also shared exposure results that would be equivalent to acrylic painting behind window glass, or indoor exposures. Their conclusion was the resistance of this polymer material to photo-chemical degradation by near-ultraviolet light is very high. In its photochemical stability and retention of mechanical properties, it can be a considered a ‘Feller Class A’ polymer material, and this probably derives both from the intrinsic stability of the acrylic polymer and from its high original molecular weight. After two hundred days of UV-A exposure this would have been a dose of near ultraviolet light–the equivalent of about 5000 museum years. Five thousand years! We’re talking about accelerated aging studies, which are not the same as 5000 years of real exposure, but even if we reduce this prediction five fold we still have a material of exceptional quality.
BRAD Do additives such as retarding medium affect the paint film? Are there other conventional acrylic additives that will cause the paint to crack or discolor over time? Do spray acrylic varnishes discolor? Should artists avoid acrylic sprays?
MARK There are many additives in acrylic paint. Painters who are curious about these additives should read the online version of Modern Paints Uncovered from the symposium held at The Tate in 2006 in London. We have a longer response as well in our JustPaint.org archives, The Acrylic Patina.
As for spray varnishes, we have evaluated quite a range on the market. Beyond our Archival Aerosol Varnish and our MSA Varnish, which have continued to perform quite well, Lascaux’s UV Varnish Gloss, Optima Millennium, and Schmincke’s Glanzfilm are also performing at acceptable levels.
BRAD One reason I shifted from oil to acrylic with my abstracts was because the oil paints in thick applications were drying with a weird alligatoring texture. It could take months for the effect to show but there was nothing I could do to stop it. So I switched to acrylics and greatly enjoy the expanded textural possibilities. Are there any archival dangers from applying too many layers of paint or too much texture in acrylics?
MARK We haven’t found any problems with multiple applications or textures with acrylics. I think this is where acrylics perform the best. The only difficulty can be that artists are experimenting with thicker and thicker clear applications. These thick applications will not remain perfectly clear or colorless over time.
Another problem with very thick applications is not giving the acrylic paint enough time to fully dry. As skin forms over the acrylic paint it’s more difficult for all the volatiles to release. As you paint thicker it simply takes longer for this process to resolve. Because of the wonderful flexibility of acrylics the newly painted film continues to remain extremely soft. Artists who move their thick paintings (½ inch or more) after just a few weeks of drying may see cracking as layers underneath haven’t had time to coalesce and form strong enough bonds.
This softness becomes an issue when shipping or storing and is exacerbated by thicker applications simply because it’s more difficult to pack and keep the thickly painted surface from contacting other surfaces or packing materials. Another problem with the soft surface is that it can be more easily marred than the harder oil paint film–another reason to keep the painted surface separate from other surfaces while storing or shipping.
BRAD I occasionally add sand, chalk, or pieces of paper to paint applications to add texture. Are there any archival problems these additives might cause?
MARK Over the years many artists have shared their acrylic experimentations with us. Acrylics are incredibly versatile and can withstand a range of additives. One needs to be cautious about adding too many solids as the best acrylics are only up to about 50% acrylic solids and can’t withstand the level of pigment or additives that oil paint can stand. For us in formulating acrylics it’s important not to exceed the Critical Pigment Volume Concentration (CPVC). Which means not adding so many solids that important properties of the acrylic binder are lost. If you’re at all concerned about excessive solids add some additional acrylic binder into your mixture. Test your experimental mixture on a Polyethylene sheet or wax paper and allow it to dry. Then take a look at the flexibility of the resulting paint mixture. Always mix these materials well into your paint. Otherwise you’ll end up with pockets of unmixed solids that will create cracking in the resulting mixture.
Many artists have added materials such as food, plants, or other organic matter. The acrylic will not encapsulate these materials in a non-porous wrapping and these materials will spoil.
BRAD I’ve read that Zinc White in oils should be avoided as it cracks in pure applications as well as in mixed paint films. This is observable in the skies and light areas in many paintings of the French Impressionists. Is Zinc White a safe color to use in acrylics?
MARK This is a question at the edge of our understanding of pigment binder interaction–especially in oil paint. Zinc is an amazing pigment for its ability to shift tints while maintaining a color balance that is not possible with the powerful tinting strength of Titanium Dioxide. The problem with Zinc in oils is the level of embrittlement of the resulting film.
In acrylic the film is so flexible that this is not currently an issue. It’s possible there are other critical interactions that we’re not yet aware of but so far the Zinc White in acrylic has held up quite well.
BRAD I occasionally sand the surface of my abstracts using wet-and-dry sandpaper blocks or an electric sander. Are there any archival issues with the heat generated by sanding?
MARK The best way to sand acrylics is to use a wet sanding technique. This keeps the dust down and, more importantly, is a much quicker way to sand the acrylic film. A recently painted acrylic (less than 4-6 months old) is still very sensitive to water. If you wet the acrylic surface at this point it dramatically swells the acrylic polymer making it incredibly easy to sand the surface to a perfect finish. Sanding the acrylic without water, especially with an electric sander, creates excessive heat.
BRAD I love Golden Colors’ innovative mediums such as Fiber Paste and my current favorite, Clear Tar Gel. Are there any new products on the horizon you can share with the readers of Thick Paint?
MARK I do have favorites and my current favorite is a product we’ve only released on a limited basis, Thick Gesso. I love troweling this material on and sanding it to a porcelain finish. We released our Coarse Molding Paste a year ago and this allows a level of texture between our Coarse Pumice and our Fine Pumice. Another favorite custom product is a paint line that never caught on, called Paste Paint. You can only use it with a heavy duty palette knife or trowel. Imagine the thickest smooth peanut butter–probably a throwback to my childhood!
BRAD I love the Coarse Molding Paste, too, and I will definitely be looking for the Thick Gesso. I definitely want to give Paste Paint a try sometime. They both sound intriguing.
Your insights are much appreciated, Mark. Many thanks for taking the time to answer these questions.
Brad Teare –April 2016
Your insights are much appreciated, Mark. Many thanks for taking the time to answer these questions.
Brad Teare –April 2016