Oil Paint—History and Technique

Oil paint has been used since Classical times for decorative painting, for example, embellishing furniture. In the 15th and 16th centuries Flemish and Venetian artists employed a combination of tempera and oil mediums in easel painting. Oil painting was not the invention of anyone of these artists but a gradual development through the experiments and recipes of many artists. Other important factors in the adoption of oil painting were the invention of new methods of purifying linseed oil and the more widespread availability of turpentine. By the 17th century, oil painting had become the predominant printing technique in Europe—a position it maintained into the 20th century.

Whereas the technique of tempera painting is fairly standard, oil painting techniques seem unlimited. In fact, one of the principle advantages of oil over tempera is its flexibility, both in methods of application and the wide range of resulting effects. Another advantage oil painting has over tempera is the ability to use lightweight supports, such as canvases. To prepare a canvas, the artist first stretches the fabric over a wooden frame and tacks it in place. She moistens the fabric with water, then tightens it and restretches it across the frame. This process helps to prevent any slackness in the canvas.

Since the fabric would rot if it came into direct contact with oil, the artist coats the canvas with sizing—usually rabbit-skin glue. After the size dries, the painter or studio assistant applies several thin, even coats of gesso to produce a uniform texture.

The oil paint itself is thinned with turpentine and possibly varnish and more oil when it is applied to the canvas. Since oil dries slowly, the paint can be manipulated and mixed on the canvas to produce very subtle transitions between colors. Stiff bristle brushes made from pigs' bristles as well as soft sable brushes are suitable for oil painting.

In traditional easel paintings, the artist begins with an underpainting in tempera or oil which lays out the basic composition of the painting. This underpainting may be in tones of gray (grisaille) or in colors chosen to heighten the final colors of the work. For example, a white or yellow might be painted under an area that is to be a bright red, while a green  would be put under an area that is to be a dull, cool red. The artist then produces his paintings either in a series of thin glazes or "alla prima" (all at one time).

Renaissance artists usually painted with layers of glazes which gradually built up the forms and desired depth of colors. Each layer of paint was often separated by a coat of varnish to produce a more luminous effect.  Varnish was also brushed over the finished painting as a final protective film. These varnishes were often tinted to unify the colors in the  painting. Rembrandt van Rijn, for example, used golden glazes.  

In the 17th and 18th centuries, many artists, such as Peter Paul Rubens, began painting "alIa prima". These paintings were executed over an underpainting but in a much freer style than the older method of glazing. Details and  strong colors were added last. In this period artists also began using thickly applied areas of paint (impasto) to achieve their effects. The glazed technique continued to be used by some artists and was often combined with more loosely painted areas in a single painting.

In contrast to the Old Masters, the Impressionists often did not employ an underpainting. Nor did they blend the colors to produce the graduated harmonies favored by their predecessors. The Impressionists applied color in short brushstrokes, placing contrasting colors directly next to one another, flattening the forms the Old Masters had worked to build up.  

Present day oil painters use a variety of techniques. Oil paintings dating to the 1950s are characterized by the use of direct painting onto the gessoed canvas (without an underpainting), the use of very loose brushstrokes, and heavy, sculptured. impastos. More recently, many artists have rejected the expressionistic emphasis on the brushstroke and painted large untextured areas of color. Some have employed a spray-gun to apply the paint and completely eliminated any use of the brush.