Painter’s Toxicity: Part 3 – by David Molesky
When I began using walnut oil, I found it to be very thin and pale; it didn’t seem to need to be diluted with a solvent. It had a different feel from thicker, stickier linseed oil. I noticed that just using walnut oil straight as a medium made it difficult to paint in multiple layers.
I researched walnut oil in my small library of material and technique books. In Max Dorner‘s Materials of the Artists, I learned that during the Renaissance nut oil and linseed oil were both used equally, in fact da Vinci used nut oil frequently and has written about its use. The text also verified that when using walnut oil, it isn’t necessary to dilute the oil with solvents for use as a medium and it is not needed for clean up. Its viscosity is lower than that of linseed oil, and it can generally incorporate more pigment into paint when used as a binder. The chemist Tingry noted in the mid 19th century that nut oil is more weather and UV resistant than linseed oil, despite forming a somewhat softer paint film. Walnut oil has a shorter shelf life than other oils and can spoil, which da Vinci also notes in his texts.
Walnut Oil as Medium
It is common practice to use straight walnut oil as a medium without the addition of solvents. The only problem with doing that is it limits the range of fat to lean and therefore the amount of possible layers. It is important when creating an oil painting of multiple layers to have some consciousness of the fattiness of the pigment vehicle – the substrate which suspends the pigment color which is also the binding agent that adheres it to a surface. When the successive layer is leaner than the layer preceding it the new paint layer will tend to bead up and not spread properly. This was the main problem I ran into when using only refined walnut oil as a medium. This scenario can be avoided by providing tooth for the preceding layer by giving the painting surface a sand and then wiping it off with a slightly oiled rag just before you paint the next layer. This is a nice way of working because it assures that you have a textured tooth to bind the next layer and preps the surface in such a way so that it is not too dry, allowing the next layer to go on lusciously. This is the traditional way in which indirect oil painters work. Will Wilson who has mastered indirect oil painting using homemade maroger medium always sands before reworking an area in a painting.
Even with sanding between layers, there needs to be a way to increase the fattiness of the vehicle of successive oil layers. The ability to layer methodically over a period of years is the one aspect of the medium that is not afforded by other approaches to image making. Take the historical example of Titian who it is rumored used up to 40 glaze layers in his late pictures.
While I was working with straight walnut oil, one of the adjunct professors at San Francisco Art Institute recommended I try adding larch turpentine to make the final layers more fatty and to allow me to more easily glaze on top of the layered paintings. It is true that as an additive into the final layers, a balsam such as larch or venetian turpentine (venetian is just larch diluted with turpentine) can make for a luxurious stroke where the color seems to be suspended in honey. The only problem is that it contains some pretty harmful aromatic compounds. Although I still keep a little jar of this medium around it’s only there as a secret weapon when I need a super transparent glaze. Luckily, through a serendipitous studio visit, I came across another method to fatten my walnut oils, to serve as a step in between the straight walnut oil and the glazing medium that contains larch/venetian turpentine.
During Bushwick open studios I was visited by a paint maker who intended to sell me his products but unknowingly taught me a useful trick that has informed my painting practice. He told me how his line of handmade walnut oil-based paints were special because they had a wonderfully viscous body to them and were not runny like some other oil colors made using walnut oil. He said the secret was that his company thickens the walnut oil for two weeks in crock pots before using it to make paint.
I usually purchase my walnut oil at my favorite supply shop in New York – Kremer Pigments. Located on 29th street on the edge of the garment district and Chelsea gallery district, Kremer is like a bulk food supplier for painters. Not only is it a cost effective way to get supplies but you can avoid the tacky packaging, product pushing culture, and made in China garbage one might usually encounter in most chain art stores.
I found the sun-thickened walnut oil to be quite expensive, about $40 for 100 ml compared to 1L of refined walnut oil for $25. I remembered I had this tiny crockpot designed for heating dipping sauces like fondu, that had come with a larger crockpot I got for Christmas one year from my mother. So I set about giving it a whirl to thicken the refined walnut oil from Kremer. Remembering some of the finer points mentioned by the paint maker to ensure good results, I set to work making my own set-up for thickening oil.
I poured the cold pressed oil into the small crock pot up to the level of the lid, closed it and turned it on. The idea when thickening oil is that you don’t want to allow the oil to react too much with oxygen because then you’ll have a bunch of gooey bits of oxidized oil floating in the liquid oil.
I was quite satisfied with the results of my first trial. The thickened oil was fatter and thicker than the refined walnut oil. I now use this home brew as a key ingredient in my strategy to work up layers, lean to fat. For example, I might start with no medium on an absorbent ground and then begin adding a bit of refined walnut oil, followed by a greater proportion of thickened walnut oil. This approach has worked well for almost a decade.
More recently in the past few years, I have been perfecting yet another variation in the use of walnut oil that I have discovered was the secret ingredient in the paintings of Rubens, Velasquez, and others. I will discuss this in part 4 of my discussion for an approach to non-toxic oil painting.