Oil painting, painting in oil colours, a medium consisting of pigments suspended in drying oils. The outstanding facility with which fusion of tones or colour is achieved makes it unique among fluid painting mediums; at the same time, satisfactory linear treatment and crisp effects are easily obtained. Opaque, transparent, and translucent painting all lie within its range, and it is unsurpassed for textural variation.
Artists’ oil colours are made by mixing dry powder pigments with selected refined inseed oil to a stiff paste consistency and grinding it by strong friction in steel roller mills. The consistency of the colour is important. The standard is a smooth, buttery paste, not stringy or long or tacky. When a more flowing or mobile quality is required by the artist, a liquid painting medium such as pure gum turpentine must be mixed with it. In order to accelerate drying, a siccative, or liquid drier, is sometimes used.
Top-grade brushes are made in two types: red sable (from various members of the weasel family) and bleached hog bristles. Both come in numbered sizes in each of four regular shapes: round (pointed), flat, bright (flat shape but shorter and less supple), and oval (flat but bluntly pointed). Red sable brushes are widely used for the smoother, less robust type of brushstroke. The painting knife, a finely tempered, thin, limber version of the artist’s palette knife, is a convenient tool for applying oil colours in a robust manner.Source : Britannica.com