The biggest problems in oil paintings as they age are paint that cracks, paint that forms a cupping pattern over the surface, and paint that loosens or falls off the support. Most of these problems can be traced to the kind of support -- canvas or panel -- the artist chooses before applying paint.
George O'Hanlon, cofounder and technical director of Natural Pigments, a company that sells historic and natural oil paints, mediums, dry pigments, and other art supplies, taught a workshop, Painting Best Practices, at Gage Academy of Art in Seattle last week. This is the first of two articles summarizing the workshop. He estimated that 90 percent of problems of deteriorating oil paintings could be prevented by choosing the right support.
"Painting on canvas is really the worst choice you can make as an artist," O'Hanlon said. He was referring only to canvas that is stretched over stretcher bars, not canvas that is affixed to a panel. Painting on panels results in a more durable painting than painting on stretched canvas, but not all panels are equal.
In this article, I will not attempt to explain the chemical reactions of paint combined with various panels or stretched canvas, or the mechanical changes paintings undergo over time and under changing atmospheric conditions. I will offer only practical advice with some supporting evidence, intended for artists who aren't especially interested in the science behind the materials, but who care about the longevity of their works. For more detailed information, see O'Hanlon's technical articles.
Below is a list of panel materials, from least durable to most durable, along with a few of their distinguishing characteristics:
Solid wood expands and contracts much more than the dry oil-paint film in response to changes in temperature and relative humidity. It also expands at different rates in different directions, unlike the paint film. This can contribute to delamination, or paint layers separating from the panel over time. Solid wood panels are better than stretched canvas, but there are better choices.
Plywood is made with urea formaldehyde, which is an excellent adhesive between layers of wood, but it creates fumes that are bad for oil paint. Plywood is also highly absorbent, so it must be treated with an impermeable "size" or barrier. Then the ground (often called gesso) can be applied. The paint layer must be protected from the panel's tendency to absorb other substances. Also, plywood's inner layers contain knots, which create uneven tension and mechanical stress for paintings.
Fiberboard: This popular support also contains urea formaldehyde resins to keep the fibers together. It's strong and hard, but needs to be protected from getting wet, which causes the fibers to lift. It also can be damaged. If, for example, the panel is dropped, a corner could shatter. Imagine that an ordinary household object, like a shelf made of fiberboard, is dropped. It isn't catastrophic. If a family heirloom painted on fiberboard is dropped, it is catastrophic. An example of fiberboard is medium-density fiberboard, also known as MDF.
Hardboard is similar to fiberboard, but denser. It shares the same characteristics as fiberboard. Examples of these panels, available in art-supply stores, include Gessobord and Claybord. The manufacturer, Ampersand, says on its website that its boards are made without formaldehyde.
Plastic is rigid and lightweight, and doesn't absorb much moisture. That's the good news. The bad news is that it's susceptible to damage by ultraviolet rays. Plastic also doesn't welcome paint to its surface without some kind of adhesive ground. Many artists will recoil when faced with the possibility of using traditional paint and painting techniques on plastic panels, but such materials, including polyvinyl chlorine (PVC) and polyethylene, do show promise for durability.
Metal and metal composite: This category includes copper, aluminum composite material, and aluminum honeycomb panels. This category offers the most durability for oil paintings. The panels are strong and lightweight, and they don't expand or contract with normal changes in temperature or relative humidity, and some of them are easy to fabricate. Aluminum honeycomb panels, the very best type of panel, are expensive and hard to find. This makes copper and aluminum composite material the most practical choice for artists and art students who care about durability but need to procure their panels easily and get back to work at their easels.
"Oil paint has an affinity to copper," O'Hanlon said. "You can paint right on it." The bright gleam of new copper is alluring to artists who like to paint with transparent colors over a reflective surface, but the gleam doesn't last. Copper oxidizes, turning dull brown over time, through exposure to oxygen. Coating the copper with lacquer will slow oxidation, and scuffing the surface will aid with paint adhesion.
The panel that combines the most practicality, affordability, and durability is aluminum composite material (ACM). It's composed of thin sheets of aluminum around a polyethylene core. It's lightweight, rigid, and stable. Standard-size panels aren't sold in most art-supply stores, but they are sold by Natural Pigments. (I also bought a 4-foot-by-8-foot sheet of ACM at a plastics supply outlet, which I cut myself. To learn more about the process of purchasing ACM, cutting it without power tools, and priming it, watch my video.)
O'Hanlon was trained as a fine artist, and he developed an interest in professional-grade art materials over time, consulting with scientists, scientific writings, conservators, and conservation writings to learn how materials interact with each other, with air and moisture, and with time. He and his wife, Tatiana Zaytseva, co-founded Natural Pigments in 2003 in their garage. The company has expanded into a 10,000-square-foot building with five employees, and the owners anticipate expanding again next year. Natural Pigments is located in Willits, California.
Other topics in the Painting Best Practices workshop included grounds, paint, mediums, and varnishes. Next week I'll post an article about these topics.
Author's note: Thanks to Gage Academy of Art for awarding me a scholarship, which made it possible for me to attend the Painting Best Practices workshop.