This oil began with a pet theory, always a little dangerous. But it seemed that several different older Dutch painters had access to a medium that was somewhat gelatinous: it flowed but also held. What was it? The usual answers to this question involve a resin. But resins don't show up in modern conservation research nearly as often as they show up in the many theories of scholars and purveyors. After abandoning resins -- and solvents -- for the chalk and oil putty medium, I began to work directly with the oil. The more experience accumulated in the context of 17th Century formulas, the more it began to seem possible that this mystery medium was simply an oil which had been specifically modified. But how? Many experiments were subsequently undertaken to try to create an oil with the right characteristics using period materials and techniques. This took several years, using the formulas in the De Mayerne manuscript as a point of departure. While there are several related lead technologies which produce a somewhat modified and thicker oil -- see oil formulas for more on this -- I kept returning to working with the simplicity of the metal itself.

       If a thin layer of oil is put in a lead tray open to the air, a complex series of reactions take place over time, resulting in an oil which is thick and polymerized on the one hand, but with a different rheology than stand oil or sun oil. This process takes several months at room temperature, I've let it go as long as seven months. Up until a very thick viscosity, this oil has the unique characteristic of both holding and sliding.

      The oil produced by this process has significantly more body than raw oil, but is not sticky or glutinous like stand oil or sun oil. It begins cloudy, but clears over time. The cloudy oil dries transparently, however.

      Used quite thick, this oil can be used to make white lead paint seize. A very small amount will immobilize a large amount of handmade white lead paint, turning it into an impasto paint with no other ingredients.

      On the right, handmade lead white paint and a small amount of thick unsun oil.

      When the unsun oil is mixed into the paint, the rheology changes dramatically.

      But a cold leaded oil which is made from raw oil has a significant tendency to yellow over time on drying. This is not an issue in the above application, but is a major issue in all but the opening warm layer of a painting. The material seemed like it had promise, how to keep it from yellowing became the next priority.

      If the oil is heat pre-polymerized first at a low level -- 100 to 110 C, 48 to 72 hours -- before it is introduced to the lead, no yellowing takes place in the final product. This is a procedure I began doing in an attempt to artificially age the oil, "old" oil being universally feted in the older texts. This is a slightly different concept than the "semi heat bodied oil" from the National Gallery Technical Bulletin research into 17th Century Dutch painting. What was actually done to the oil then of course cannot be known: also the degree of heat involved. But this process results in a very useful product: the real goal.

      On the right, the relatively thick skin from a jar of unsun oil. Much thicker than would be used in actual practice. Not quite fully dry, some spots still have a bit of cloudiness.

      Another image of a holding jar of thick unsun oil, showing the way it dries clear and without yellowing.

      Unsun oil can be used at several different viscosities. When thinned with spike lavender or pre-polymerized oil it becomes a family of mediums which can function in any number of ways . At the thicker end of the scale, it can be effective in a rich, broken surface alla prima style. The thicker oil can also be cut with heat pre-polymerized oil to produce a range of working oils for painting. In practice for layered realism, unsun oil cut with two parts of heat pre-polymerized oil works well for all but the final layers, when a one to one cut is used. These materials are similar in character to the Oil of Delft family of recipes created by Donald Fels, except that they are less glutinous, more mobile and gelatinous.

      Various types of unsun oil. It's not going to win any beauty contests, another reason I think it might in fact be a material of importance before painting entered its more self-consciously aesthetic phase. The three on the left are thick and uncut, these very slowly clarify and throw a precipitate over time. The middle jar is cut one to one, and is clearing of the lead salts. The larger jar on the right began with a very thick unsun oil and was cut two to one. It then cleared very quickly. While uncut unsun oil may be cloudy, it dries with great depth and brilliance.

      Yellowing test several months old done with a variety of unsun oils made with walnut oil.

      A batch of unsun oil which is in the process of gelling.

      The same gel a few weeks later, relatively uniform and firm. Made with lead metal, heat, and walnut oil.

      This work was carried out using refined walnut oil. The behavior of refined linseed oil in this context is now beginning. This material already appears to behave very differently when exposed to lead metal. Image shows refined Swedish linseed oil which dramatically thickened on lead in a few weeks, was then cut one to one with spike lavender. In the process still of settling out, clear oil has been poured off the top for use. Yellowing test several months old at left. This oil behaves a lot like damar, sets quickly, dries very fast.

      4-09: As an offshoot of various methods used to refine organic, cold-pressed linseed oil, experiments have been ongoing in making an unsun oil with unrefined linseed oil as well. Pictured here is the unrefined oil used to make the unsun oil below. This is from Azure Farms in Oregon, a very low acid oil, aroma like a field of flowers. Relatively inexpensive, certainly compared to retail nutritional oils, especially in bulk.

      The final product. About the consistency of stand oil or moderate sun oil. Could be made thinner or thicker. Less sticky than sun oil, dries faster. Procedure was to wash the oil, then place in a thin layer in a lead tray exposed to oxygen but protected from dust. The oil remained in the tray for a month with occasional stirring. It threw no sediment of break. This oil dried hard overnight at 18C. Living in a northern climate with variable sun in the summer, this is a perfect material to make instead of sun oil. It takes a while to begin the process, but a dozen batches a year adds up. For a pdf about the washing procedure, go here.

      Commercially available oils can also be processed using a lead tray. There's also the possibility of using copper as Cennini discusses. The initial use of a copper tray may produce a green oil. In my experience, this oil will turn brown and yellow. However, repeated use of the tray results in a light oil which does not yellow.

      Close-up photo of Graphic Chemical Burnt Plate Oil #5 aged on lead for several months. Thickness where yellowing begins is about a quarter inch.

      Oil number one is the Allback Swedish organic cold-pressed linseed oil, aged in the light for a year. Oil number two is the Allback oil exposed to the air in the copper tray above for a month. Oil number three is Burnt Plate Oil #5 from Graphic Chemical, exposed to the air on lead for a month.

      A branch of this project has been using various methods involving lead to refine the oil in the first place. Number one is the Spectrum Naturals walnut oil heated for 48 hours to about 100C, then another 24 hours with some litharge and white lead. Number two is half and half number three and number 4/5. Number three is the Allback Swedish organic cold-pressed linseed oil heated for 24 hours to 100C, then refined with litharge, as discussed by Field and in several even older texts. This throws a decent amount of break but takes a while to do it. Four and Five are different stages of the same Allback oil with the same heat added, left open for a week in a lead tray. These get very light but can take their time clearing, below is older. Oil number two was about seeing if I could get this material to clear quickly using oil number three: yes. Number six is number seven exposed to the air for four days in a glass tray. Number seven is the Loriva unrefined walnut oil given the litharge treatment. These oils all have a lot of body for their relative resistance in use from the combination of the two different types of polymerization, one by heat, the other by the metallic oxide. While the oils refined on litharge always lose their color over time, the oil is definitely more saponified by this technique. The simplicity of the oil exposed to lead metal and air has great appeal.

      Yellowing test of oil number two above. On gessoed canvas, several months old.

      Much more is possible in terms of manipulating the oil than is ever supposed by the relatively devolved root assumptions of modern painting practice. These root assumptions are a kind of puritan reaction to the many faulty mediums and practices of the 19th Century, but do not address the core strength of 17th Century practice -- artist made materials -- because acknowledging this inconvenient truth would prove a relentless inconvenience in a contemporary academic setting.

       An organic oil is quite complex in its make-up, the behavior of chains of triglycerides (image here) has been studied by generations of organic chemists. Painters have unfortunately become used to thinking in terms of their materials in the tidy, discreet compartments defined by commerce. But incredible variations exist between the raw oil and stand oil of the art supply store. While oil in which the triglycerides are cross-linked through heat is still part of the general awareness, oil in which the triglycerides are linearly polymerized -- as on lead metal -- is not. When these two modes of polymerization interact, unusual rheologies occur in the oil, rheologies that have left centuries of painters and writers thinking that resins or other nostrums -- Constable's term -- must have always been involved in 17th Century practice. But, as anyone who paints on a daily basis can attest, the simplest technical system at the easel is the most efficient in both internal and external terms. Is the interaction of these two modes of polymerization then part of a process for modifying the oil that was lost? Perhaps, but the very nature of the material itself means that this can never be known with any certainty. It seems more important to offer that once the limited attitudes of commerce and modern painting practice are left behind and the materials are addressed on their own terms, the development of greater facility in handling them is simply a matter of observation and logic within the cultural gestalt defined so clearly by the De Mayerne manuscript. This is not about finding out what a given older painter used so much as it is about reversing the prevailing commercial devolution and reconstructing a living, artisanal craft that makes demonstrably better paintings.