The most fundamental technology lost from older painting is how early painters refined and modified their oil. Later, as commercial tube paint made with raw oil became more and more prevalent, so did various resin or resin and oil mediums designed to alter the behavior of this paint. “The Artist’s Assistant” by Leslie Carlyle makes it clear that in 19th Century England, the search for the older manner of painting resulted in a virtual minefield of complex materials. However, the research carried out by the National Gallery and reported in their yearly Technical Bulletins consistently suggests that very little resin was ever used, that most of this was soft — i.e. larch balsam — and that the use was in “small amounts,” possibly fused into the oil in some cases, and that the use of resin is never global until the 19th century. This is logical: older painting is consistent in its technical conservatism and economy of means.
Having made and worked with amber, copal, and sandarac varnish for several years, and being somewhat attached to this technology, this simplicity was at first hard to comprehend. How could it be done otherwise? What could “the oil” do? Ultimately, in 2007, I decided it would make the most sense to learn an all-oil method in order to compare the techniques fairly.
The results of this experience suggest that two fundamentally different systems exist. The original one is based on the behaviors and rheology of hand-pressed, hand-refined oil. The modern one is based on the behavior and rheology of mechanically pressed and refined oil.
While the specific older system can never be known fully or with certainty, working with its principles via older recipes and procedures leaves no question that it offers a more functional and evolved way of utilizing the oil.
The older system naturally leads to ways of working that are unavailable to the modern one. This is because all the oils used by current manufacturers are refined according to standards for the food industry. The goal of this refining is to minimize oxidation that can cause rancidity. As such, without added driers, it is not possible to get a modern oil to dry quickly. This is not the case when beginning with an unrefined oil, where, without using lead or other metals, the potential for oxidation can be enhanced by various traditional refining methods.
In the modern system, the emphasis is on purchasing ready-made products. Science is often part of contemporary marketing strategies, but this is the selective science of the marketplace: the science of technical art history is more detached, and tells a different story. Once upon a time, the art and craft informed one another in practice. But this is not a fairy tale. Hand-refined oil still offers tremendous potential within a creative painting process.
In 2006 I began working with the organic cold pressed linseed oil from Sweden marketed by Allback. I refined it several traditional ways in the hope of getting a fast drying oil that didn’t yellow.
The first experiment was washing the oil with salt, sand, and water, a technique spoken of in many older books. This took six weeks to do, and a significant portion of the oil was lost, about a third. This process is not to be confused with the various quicker processes designed to clear a cloudy, totally unprocessed oil. Oil can also be made non-yellowing simply by traditional exposure to the sun in full glass jars, but this takes several years.
The refined oil does dry much faster than the unrefined oil, but it also yellowed slightly at first. Much less than the alkali refined oil of commerce, a little more than walnut oil. After aging in a sunny window for a year, this oil was lighter and yellowed still less, the same amount as the better quality commercial linseed oils in tests — very little. I like the slightly grippier, tighter working quality of the salt-refined oil better, but this may not be of interest for larger and smoother painting styles. I also noticed that this oil did not dry from the surface or form a skin, in spite of drying quickly, one and a half to two days. Alla prima work made on a summer morning has been dry before nightfall.
Is this process worth the effort? As with many things in painting, it depends. Salt refined linseed oil has a unique working character that helped me understand, for the first time, why linseed oil could be preferred over walnut oil by older painters. So, washing with sand and salt, a traditional method documented as far back as the 17th century De Mayerne manuscript, offers an avenue to an oil of this type. Are there other high quality linseed oils available commercially that require no further processing? Yes. But, because of the way they are processed — a process designed for edible oils, not oils for painting — they don’t dry quickly, therefore, the system the salt-refined oil creates naturally on the palette cannot occur. This becomes especially relevant in terms of further modifications of the oil, or using the putty method to paint without solvents.
A combination of several of the traditionally known factors contribute to an oil which dries faster, harder, and with less yellowing. These factors are: a high quality cold-pressed oil to begin with; refining using a traditional method, subsequent aging or preheating of the oil, and use of the oil in thin layers which will dry quickly. The one exception to the thin rule seems to be the chalk putty medium, which does not increase yellowing even when used thickly