Oil colours consist mainly of pigments and binding agents. The binders of the oil paints are drying and semi-drying oils of plant origin, for example linseed oil, poppy seed oil, safflower oil and sunflower oil.
The pigments used in artists’ oil colours are organic and inorganic, synthetic and of natural origin. The pigment palette consists of traditional as well as the most modern pigments available. The pigments used determine the colour shade, the opacity and the lightfastness of an oil colour. The quality of the raw materials used, the manufacturing process and the individual formulations determine decisively the quality of the resulting artists’ colour.
Essentially, oil colours can be used directly from the tube and without the addition of mediums or additives. This is recommended, for example, for alla prima painting, which requires the working to be fast. The use of mediums and additives extends the spectrum of oil painting techniques as well as creating the possibility to influence the consistency, the drying time or the level of gloss of the colours.
In contrast to other artists’ colours, oil colours need the oxygen in the air to dry. The binder in the oil colours, which is a composite of various oils, dries by oxidation, i.e. by absorbing oxygen. The flow of the oxygen intake and the chemical reaction associated are of vital importance for proper film formation. This process depends on the type of oils used, the pigments, the surface, the climatic conditions and of the applied layer thickness of the colour. They type of drying explains why you should plan plenty of time to produce a painting using oil colours. Oil colours need days to dry and to dry fully, depending on the thickness of the layer, several months.