Most discussions about painting supports focus on paper—not surprising since paper has been used as a support for watercolor for many centuries. A growing trend is modern alternatives, such as rigid supports with absorbent grounds. What is interesting is that nearly all the discussions focus only on the surface properties of supports rather than mechanical properties.
The mechanical properties of painting supports are as important, if not more, than their surface qualities. The former properties are rarely considered by artists. This is surprising because for at least 40 years the greatest causes of paint degradation have been attributed by conservators to the stress on paint film resulting from the expansion and contraction of the support due to changes in relative humidity and temperature.
Without question paper is the most popular support for watercolor painting today. Its popularity notwithstanding, it actually may not be the best support in terms of its mechanical properties. Paper is hygroscopic, meaning that as humidity in the air changes, canvas absorbs and releases moisture to maintain equilibrium with these changes. Cellulose fibers in paper swell and contract at much different rates than paint layers, producing mechanical stress on paint as the environment changes. Although these changes may appear to be small, over time they place enough stress on paint that leads to cracking, cupping and paint loss.
Paintings on rigid supports (stone, metal, composites, etc.) with lower response to environmental changes, such as relative humidity, typically exhibit less paint degradation over much longer periods of time, because the support does not induce as much stress on the paint film as does paper. Aluminum composite panels, on the other hand, are not affected by relative humidity, so they do not create stress on paint layers.
Artefex Panels are lightweight but rigid and durable aluminum composite material (ACM)—two strong sheets of aluminum bonded to a solid polyethylene core. The panel is coated on one side with a white polyester coil coating and a mill (polished aluminum) finish on the other side. The panels are available in common sizes up to 20x24 inches. This weather-resistant panel is ideal for a wide range of paint mediums and mounting applications.
The panel comparison chart is a good starting point if you are unsure which Artefex panel to use. It cross references mediums to the type of panel we recommend. The last six columns describe two important properties, the absorbency and texture of the surface preparation.