What is oil colour?
Oil colours have been used in various forms since the fourteenth century. Before then, pigment ground into an emulsion with egg was the medium of choice in most artists’ studios. Oil colour, however, quickly surpassed egg tempera in popularity because of greater versatility, longer working time and more subtle rendering. The rounded, exquisitely modelled forms characteristic of the Renaissance would not have been possible without the qualities that come with oil colour. Originally, the master painters’ apprentices within the studio prepared oil colours. During the late eighteenth century, colourmens’ shops appeared in Europe, offering colour that was pre-milled. In 1832, Winsor & Newton was founded in London. While there is great romance in the history of oil colour, there is also no question that today’s colours are vastly superior in quality to those made centuries, generations, and even just a few decades ago. Why? New, more permanent materials, superior methods, as well as the accumulated experience and scientific expertise of the manufacturer have made a dramatic difference to the quality of colour available to today’s artist.
Today, traditional oil colour is made through essentially the same process employed in the fifteenth century. Pigment is milled with a vehicle of linseed oil (from the flax plant) and, in some cases, safflower oil (which is paler and dries more slowly). Instead of grinding each colour by hand, using a stone or glass muller, the best quality colour is produced today using a variety of milling methods. Decisions about how many passes are required through the triple roll mill, how much oil is used, as well as the kind of oil, are all determined based upon the individual characteristics of each pigment.
The finest oils offer the following:
- Depth of colour. When milled properly, linseed oil will support a high concentration of pigment. This translates into high tinting strength, true mixing, and the opportunity to take full advantage of the relative transparency or opacity of each pigment. In addition, the refractive qualities of the oil (how light passes through the vehicle) bring a richness and jewel-like depth to the colour that is still unmatched when compared to any other medium.
- Extended working time. Depending upon the pigment, Winsor & Newton oils become touch dry in 2-12 days, allowing for extended working, blending, and modelling. The variance in drying time is due to the reaction of each pigment when mixed with the oil.
- Stability within the tube. Expertly milled colour will remain stable in suspension almost indefinitely. Colours milled with less skill have a tendency to separate, with oil rising to the top of the tube, and leaving bulk pigment at the bottom. In addition to being an annoyance for the painter, too much separation can result in colour that, when applied, is “underbound”, and that doesn’t include enough oil to create a stable paint film.
- Permanence and stability on the painted surface. The finest oil colour is an ideal mixture of pigment and vehicle, allowing for the oil to dry as it should, forming a stable film that, under the right conditions, will last for many generations.
Linseed oil dries by oxidation, a chemical process that occurs as atmospheric oxygen is added to the exposed oil film. In short, oil colours dry through a long, slow breathing process. The drying mechanism starts as oxygen is added to the oil molecule, launching a reaction that transforms the essentially linear structure of the fluid into a hardened, three-dimensional, lattice structure. When properly applied, the oil film can be highly stable and permanent. But anything that interferes with the drying or polymerisation process – whether it be over-thinning, or the use of impure solvents – will produce a film that is less able to withstand the ravages of time.