Oil painting on canvas has been around for centuries. It is a style where images are sketched directly onto the canvas and then painted over with oil-based paints. These are usually paints with linseed oil as their base, but safflower oil is another common type of oil included instead. The following aspects focus on painting with oil-based paints.
Priming the Canvas:
Once the canvas has been stretched, it needs to be primed before paint oil paints can be applied to it. This is relatively easy process and requires the purchase of acrylic gesso. If a pre-stretched canvas was purchased, then it may already be treated. It's a good idea to check when buying the canvas. There's no since spending time on this step if it isn't necessary. Be sure to shake the container well before applying it to the canvas. One coat will leave a much rougher appearance than multiple coats. Gesso will dry quickly. Make sure the first coat is dry before adding another.
Fat Over Lean:
This term refers to the amount of oil present in each layer of paint. It is important to keep track of this concept, in order to eliminate cracking of the paint when it dries. Some oil paints take a couple of days to dry while others takes a couple of weeks. This varying time is also dependent on the level of oil in the paint. Lean oil paint has less oil and dries faster than fat oil paint. So, the term Lean Over Fat is used to remind the artist to apply paint with more oil over one with less. The more layers there are on the painting, the more oil should be present in each additional layer.
Solvents and Resins:
Solvents are added to the paint to dissolve the resin when cleaning up and they are also added for changing the way oil paints work. These solvents will evaporate over time and are very flammable. Common solvents include; turpentine, mineral spirits, citrus-based thinners, and alkyd-based mediums. Turpentine is the most common solvent used and it has a quick evaporation rate. Mineral spirits have a medium evaporation rate and aren't as easily absorbed through the skin; these can also be purchased in an odorless form.
While citrus-based thinners don't have as offensive on an odor as the two previous forms of solvent, they still produce harmful vapors. There are citrus-based thinners that are manufactured out of food-grade citrus oil. Some of these are also combined with a solvent that is non-flammable and non-toxic, which is much better for the person using it. The alkyd-based mediums are great for speeding up the drying time of most oil-based paints.
Different oils allow for varying drying times in oil-based paints, as well as adding a yellowing effect to the paints. Linseed oil comes from the flax plant, dries thoroughly, and can be used with all colors. Stand oil takes a longer time to dry than linseed oil, but it provides a finish that is smooth and looks like enamel. Poppy seed oil is very pail and is often used with light colors and white, due to the less yellowing that occurs when it dries. It takes between 5 to 7 days to dry, which is longer than what it takes for linseed oil.
Safflower oil has similar properties to poppy seed oil, but it dries faster. Walnut oil is very thin and often used to make paints more fluid for use. Each artist has his/her preference to the type of oils used when oil painting on canvas.