Oil Painting

Oil painting is done on surfaces with pigment ground 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 result in different properties in the oil paint, such as less yellowing or different drying times. The oil usually takes weeks to dry.

It 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". The popularity of oil grew in 16th century Venice, where a water-durable medium was essential.

Recent advances in chemistry have produced modern water miscible oil paints that can be used with, and cleaned up in, water. These are still "real" oil-paints in every sense of the meaning. Small alterations in the molecular structure of the oil creates this water miscible property.

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. First, the artist prepares the surface. Although surfaces like linoleum, wooden panel, linen, and cardboard have been used the most common surface is canvas. Canvas is a cotton fabric with thick fibers. The artist first prepares a wooden frame called a "stretcher" or a "strainer." The canvas is then pulled across the wooden frame and tacked or stapled tightly to it. The next step is for the artist to apply a ground to isolate the canvas from the acidic qualities of the paint.

Traditionally, the canvas was coated with a layer of rabbit skin glue and primed with subsequent layers of finely ground chalk and rabbit skin glue. Later the process was changed to a priming of rabbit skin glue with subsquent layers of whiting (gypsum, chalk, barium dioxide, titianium dioxide) mixed with linseed oil. Modern gessos are made of titianium dioxide with an acrylic binder. The artist might apply several layers of gesso, sanding each smooth after it has dried.

Next the artist might sketch an outline of his intended figure, called a "cartoon." Then he begins to apply the pigment to the surface. "Pigment" may be any number of natural substances with color, such as sulfur for yellow or cobalt for blue. The pigment is mixed with oil, usually linseed oil but other oils may be used as well. The various oils dry differently creating assorted effects. Traditionally, an artist mixed his or her own paints for each project, but in the late 1800's paint in tubes became available. Artists then could mix standard colors easily to create subtle variations of hue.

The artist most often uses a brush to apply the paint. Brushes are made from a variety of fibers to create different effects. For example, brushes made with hog's bristle might be used for bolder strokes. Brushes made from miniver, which is squirrel fur, might be used for finer details. Sizes of brushes also create different effects. For example, a "round" is a pointed brush used for detail work. "Bright" brushes are used to apply broad swaths of color. 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. Some artists even paint with their fingers.

Most artists paint in layers. The first coat or "underpainting" is laid down first, painted normally with turpentine thinned paint. This layer helps to "tone" the canvas, and cover the white of the gesso. Many artists use this layer to sketch out the composition. After this layer dries, the artist will then begin to paint a "mozaic" of color swatches, working from darkest to lightest. The borders of the colors are blended together when the "mozaic" is completed. This layer is then left to dry before applying details.

After it is dry, the artist will apply "glazes" to the painting, sometimes 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 properly. Artists in later periods such as the impressionist era often blended the wet paint on the canvas without following this layering method. This method is called "Alla Prima." When the image is finished and dried for up to a year, an artist would seal the work with a layer of varnish typically made from damar crystals dissolved in turpentine.