Painting with oils is done with pigments bound to a drying oil. While many different oils are used, linseed oil from flax appears to be the overwhelming favorite. Safflower, walnut and poppy seed oils are also occasionally used. Some yellowing of the painting occurs as oils dry and the extent of the yellowing differs for different of oils. Differences in sheen may also be noticed.
Oil paintings were first done between the 5th and 9th centuries but not widely implemented until the 15th century. Oil paintings replaced tempura techniques which were most used from the 1st to the 15th centuries to produce long lasting color in paintings.
Most oil paintings are done on canvas, but can also be accomplished on many other surfaces, including linoleum, wood, panel, paper, slate, and cardboard. They begin with a charcoal sketch or a sketch using thinned paint. Paints are mixed with oil and artist’s grade mineral spirits, creating a faster or slower drying paint. These agents can also be used to clean and dry brushes.
Oil paintings are generally done in multiple layers. First, an under-painting of a turpentine-thinned paint base is added and dried. Second a mosaic of different colored zones are added. The darkest colors added first then lightest. Borders between colors are then blended into each other. The painting is again allowed to dry. This will require at least three weeks, but in some cases a painting may take up to a year to dry. After drying, significant detail may then be added and the painting completed. Thus, the painting is completed in layers. If at any stage mistakes are made or if you are unhappy with how it is developing you can scrape off the most recently applied layer and start again. Alternatively you can use rags and turpentine while the paint is still wet.
Each new layer of a painting should contain more linseed oil than the last. The lower layers will absorb oil from the upper layers and the upper layers will retain sufficient oil to keep from drying quickly. If the upper layers dry more quickly the painting will peel and crack. In general, paintings should dry to touch in about two weeks, but should not be varnished in less time that 6 months to a year. In reality art experts do not consider oil painting totally dry for up to 60-80 years.
In general, pigments and oils may be mixed on a palate and should be laid out in the same order each time. Then selection of colors becomes instinctive over time. Brushes are expensive, but there are many synthetic varieties that are inexpensive, durable and good. Minimally one needs a flat brush for broad color application and a round pointed brush for detail.
Do a simple painting first. Later you can add to your collection of brushes, pigments and other tools. You can read about basic strategies for oil painting on the Internet, in books from the local library or a book store. Just as with drawing with pencils and water colors, you should concentrate on doing enough to get started and then add to your approach and level of sophistication as you proceed.