oil painting - Process of oil painting

A method of painting which employs drying oils (such as linseed oil) in the medium. In use since Roman times for decorating shields, etc, the technique was perfected and adapted to painting pictures in the 15th-c.

Oil painting is done on surfaces with pigments that are ground and mixed into a medium of oil — especially in early modern Europe, linseed oil. Other oils occasionally used include poppyseed oil, walnut oil, and safflower oil. These oils give various properties to the oil paint, such as less yellowing or different drying times. Certain differences are also visible in the sheen of the paints depending on the oil. Painters often use different oils in the same painting depending on specific pigments and effects desired. A basic rule of oil paint application is 'fat over lean.' This means that each additional layer of paint should be a bit oilier than the layer below, to allow proper drying. Traditional oil painting techniques often begin with paint mixed with turpentine. As a painting gets additional layers, the paint must get oilier (leaner to fatter) or the final painting will crack and peel. There are many other painting mediums that can be used in oil painting, including cold wax, resins, and varnishes. These additional mediums can aid the painter in adjusting the translucency of the paint, the sheen of the paint, the density or 'body' of the paint, and the ability of the paint to hold or conceal the brushstroke. These variable are closely related to the expressive capacity of oil paint. When looking at original oil paintings, the various traits of oil paint allow one to sense the choices the artist made as they applied the paint. For the viewer, the paint is still, but for the artist, the oil paint is a liquid or semi-liquid and must be moved 'onto' the painting surface. Traditionally, moving paint was accomplished with paint brushes, but there are other methods, including the palette knife, the rag, and even directly from the paint tube. Oil paint remains wet longer than many other types of artists' materials, so a reality in many painter's studios is the removal of oil paint from the painting. This can be done with a rag and some turpentine for a certain time while the paint is wet, but after a while, the hardened layer must be scraped. Oil paint dries by oxidation, not evaporation, and is usually dry to the touch in a day to two weeks. Art conservators do not consider an oil painting completely dry until it is 60 to 80 years old.

Oil paint was probably developed for decorative or functional purposes in the High Middle Ages. Surfaces like shields — both those used in tournaments and those hung as decorations — were more durable when painted in oil-based media than when painted in the traditional tempera paints.

Many Renaissance sources credit northern European painters of the 15th century with the "invention" of painting with oil media on wood panel — Jan van Eyck is often mentioned as the "inventor". Oil painting was ideal for the northern European painters, because the preferred fresco painting media did not work as well in their cooler climate. Recent advances in chemistry have produced modern water miscible oil paints that can be used with and cleaned up with water.

A still-newer type of paint, heat-set oils, remain liquid until heated to 265–280 °F (130–138 °C) for about 15 minutes. Since the paint never dries otherwise, cleanup is not needed (except when one wants to use a different color and the same brush). Although not technically true oils (the medium is an unidentified "non-drying synthetic oily liquid, imbedded with a heat sensitive curing agent"), the paintings resemble oil paintings and are usually shown as oil paintings.

Process of oil painting

The process of oil painting varies from artist to artist, but often includes certain steps. The next step is for the artist to apply a ground (or size) to isolate the canvas from the acidic qualities of the paint. The gesso layer will tend to draw the oil paint into the porous surface, depending on the thickness of the gesso layer. Excessive or uneven gesso layers are sometimes visible in the surface of finished paintings as a change in the layer that's not from the paint. The pigment is mixed with oil, usually linseed oil but other oils may be used as well.

Traditionally, an artist mixed his or her own paints for each project. This changed in the late 1800’s, when oil paint in tubes became widely available. Also, the portability of tube paints allowed for plein air, or outdoor painting (common to French Impressionism).

The artist most often uses a brush to apply the paint. The artist might also apply paint with a palette knife, which is a flat, metal blade. A palette knife may also be used to remove paint from the canvas when necessary.

Most artists paint in layers, a method first perfected in the Egg tempera painting technique, and adapted in Northern Europe for use with linseed oil paints. The first coat or "underpainting" is laid down first, painted normally with turpentine thinned paint. After this layer dries, one way the artist might then proceed is by painting a "mosaic" of color swatches, working from darkest to lightest. After it is dry, the artist will apply "glazes" to the painting, using a process of "Fat over Lean" which means more oil/paint ratio than the previous layer. A classical work might take weeks or even months to layer the paint. Artists in later periods such as the impressionist era often blended the wet paint on the canvas without following the Renaissance layering and glazing method.