We get a lot of students asking us about oils… and what are the differences between all those golden bottles that are neatly lined up on the shelves of the art supply stores. I was given only a finite amount of information by my professors who usually had us use what they used for their own work. But rarely did they explain why. A few years ago, with my curiosity piqued, I headed over to the art supply store to do some research of my own.
The store shelves were lined with linseed oils of all types: refined, cold-pressed, bleached, raw, sun-thickened, and stand oil. I saw walnut oil, poppyseed, and safflower oil too. The list continued with driers and siccatives, hard resins, soft resins (or varnishes), synthetic resins, balsams, essential oils, and waxes. If you’re thinking this looks more like a materials list for a chemistry class, you’re not too far off. With so many choices, how do we as artists make sense of them, and how do we know which ones to use?
The answer isn’t always clear, but in most cases the role of oil in painting is fairly simple: to serve as a vehicle and binder for pigments. I like to use watercolor painting as an example. Most of us have used watercolor as kids because being water-soluble, it’s easy to clean up. The vehicle for watercolor painting is water. It helps push the pigment around on the paper, extending it, manipulating it, creating beautiful effects that are characteristic of watercolor paintings. For oil painting, the same principle applies but the vehicle is oil. That’s what “medium” is: it’s the stuff that carries the pigments around on your canvas and holds them in place when it’s dry. Oil painting medium can seem more complex because oils (and other ingredients) come in many different forms, and thus offer more possibilities for painting.
So let’s start with the most common binder of oil paints – linseed oil.
Since the middle of the sixteenth century, linseed oil has been used as a vehicle for paint. The principal advantages of linseed oil are its durability (it forms a tough, flexible skin when dry), its versatility (it can dry thick or thin, transparent or opaque, glossy or matte, slowly or quickly, etc.), and its commercial availability. The disadvantages are the eventual yellowing of the oil and the possible cracking or flaking of the paint film. These can be reduced or removed by the correct handling of the highest quality materials.
Linseed oil is also known as flaxseed oil as it is derived from the dried ripe seeds of the flax plant. I love pointing out how useful the flax plant is for painters. It provides oil for the paint, and fiber for the manufacture of linen which is a common support for oil paintings – two important functions in the creation of artwork served by a single plant. The oil is obtained by pressing, much like olive oil, or in some cases, extracted by the use of solvents. Linseed is one of a category of oils called “drying oils” due to its high concentration of a-linolenic acid which reacts with oxygen and polymerizes when exposed to the air. The tough film that results is what makes linseed oil so useful for painting – this dry oil can last for centuries.
In the coming weeks I’ll write further posts about oil and painting medium, and do my best to take some of the mystery out of the more common ingredients by discussing what they are and how we can best use them.