To prepare the mediums for my oil paints, I let linseed oil and walnut oil thicken in sunlight, sometimes a year or two, so they become “grabbier” on canvas. I discovered this do-it-yourself approach for making heat-bodied oils through the Art in the Making book series, published by the National Gallery of Art, London. Sun-thickened oils are expensive to buy and significantly cheaper to make.
There are several ways to sun-thicken oils, but they all follow the same principle: expose the oil to oxygen and sunlight while protecting the oil from insects and other debris. When I create my heat-bodied oils, I use one of two different processes—sun thickening or aging—depending on the degree of viscosity I prefer. I enjoy being able to tailor the viscosity of my oils to my working methods, and hot, dry California summers are perfect for these processes.
Above are batches of refined (not raw) linseed and walnut oils thickening in the sun to achieve a honeylike viscosity. When I say “refined oils,” I’m not referring to the alkali-refined oils of commerce nor to refined oils you might find at any art supply store. The oil to be placed in the sun for thickening should be “artist refined;” that is, a raw oil which has been cleansed by the artist of it’s mucilage and sufficiently organically refined. The sturdy picture-frame glass sits atop the pine frame, separated by thin spacers, which allow for sufficient airflow. Once thickened in this way, the oils have the consistency of honey or taffy.
If I prefer less thick oils, instead putting them through the sun-thickening process, I’ll age them on a sunny windowsill. Above you see various refined oils, ranging in viscosity, aging in this way. Letting oils thicken on a windowsill modifies them more slowly and subtly, allowing me to tailor them to more fluid, free-flowing consistencies. The amount of time I age the oil depends on its intended use on the palette. The more viscous (less fluid) I need it to be, the longer I’ll let it sit. Some of my oils have been aging for two years!
I occasionally expose my “aging” oils to oxygen by means of covering the opening of the jar with cheesecloth. The frequency with which this is done is usually determined by two things: how thick I want the oil and the rate at which I think I’ll be using the oil. I’m careful not to over-expose oil that I know I won’t be using any time soon or that I’ll be using only sparingly. This is because the oil will continue to oxidize in the jar (even if it’s closed) due to the ever increasing amount of air that gets trapped in the jar with every use. As the oil level drops, more air is introduced. This phenomenon is more dramatic over the coarse of several months and less pronounced over the course of days.
Whichever process I use for creating my heat-bodied oils, once I feel they’re the proper consistency, I must guard them against further oxidation or they’ll continue to stiffen.
While I employ certain historical techniques, such as creating my own heat-bodied oils, I don’t believe in following the Old Masters to a fault. When artists fail to take from their own experiences, they speak with an affected accent—a borrowed visual language. If your experience has been a deep one, a new language is born of it.
Award-winning southern California artist Julio Reyes is represented by Arcadia Fine Arts in New York City. Visit his website at www.julio-reyes.com.
Learn more about Julio Reyes and his work in the May 2011 issue of The Artist’s Magazine, available at www.northlight.com.
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