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Introduction
Oil paints are made from pigments ground in a drying (or semi-drying) oil, such as linseed, nut, poppy or safflower oil. The use of oils like these as binding mediums gives oil paint its characteristic appearance and its qualities of easy handling. Pigments ground in oil have a distinctive depth and colour resonance, and can be used in a wide range of techniques. These encompass transparent and opaque painting and include direct wet-into-wet painting methods, and those that work by building up a painting carefully, layer by layer, according to a prescribed system.

Oil painting can be applied in thin, transparent glazes or in thick, impasted strokes. It can be worked whilst wet on the surface of the support for far longer than other painting media, allowing scope for particular blending effects and for the safe introduction of fresh colours. In oil painting, the colour laid down wet is effectively the same colour when it dries, which makes some aspects of the medium much more straightforward than similar aspects of gouache or acrylic painting.

The History of Oil Painting


Oil painting dates back to well before the Van Eycks, who have been popularly credited with the discovery of the technique. The middle German Strasburg Manuscript (an art treatise of the Middle Ages) gives detailed instructions for the preparation of a cooked and sun-bleached drying oil with which to grind and temper pigments, and also for a cooked oil and resin varnish, three drops of which are added to each colour presumably to add manipulation. Cennini, who is more detailed on egg tempura techniques, also includes instructions for the preparation of a drying oil. The use of a drying oil as a painting medium was initially more popular in Northern Europe than in the South. The use of oil-ground colour became increasingly popular in Venice during the 15th century, and by the early 16th century it was the accepted medium for easel painting throughout Italy and the rest of Europe.

Mediums and Techniques


Oil painting need not be the complex undertaking that is suggested by the vast range of recipes for oil painting mediums and varnishes. Perfectly acceptable results can be achieved simply by unadulterated pigments ground in oils, and diluted with turpentine or white spirit as necessary, and only painting over a layer of paint whilst it is still wet or after it has dried.

Some techniques and effects do require the modification of the straight oil colour, but most can be reproduced using the simplest and soundest formulations. Some commentators claim to be able to identify the precise materials used by an artist simply by being able to copy the effect. However, it often remains difficult to identify from small paint samples, the exact nature of the painting or glaze medium used.

Binding mediums, mediums and diluents
Binding mediums also known as 'vehicles'(usually linseed oil) hold the pigment in suspension and attaches it to the support.

Linseed oil
This widely used drying oil acts as both a vehicle for grinding pigments and as an ingredient in oil painting mediums. It has been claimed that the 'suede effect' (where brushstrokes made in one direction appear different in tone from those made in the opposite direction) is removed by the use of cold-pressed oil. In fact the effect is not related to the oil but to stabilizers used in the colour.

Other forms of linseed oil, such as stand oil, sun-thickened oil, are used as painting or glazing mediums on their own, or in conjunction with other materials. They are more reliable on their own where they can be diluted to a workable consistency with an essential oil such as turpentine or, for slower drying, with oil of spike lavender. Stand oil is somewhat slower drying than sun-thickened or sun-bleached oil, but is recommended for its non-yellowing characteristics and the fact that it retains a certain flexibility with aging.

Nut oil
Made from walnuts, ths is paler than linseed oil and recommended for use with the paler pigments. In the 17th century, Henry Peacham recommended it for use in whites for ruffs and linens.

Poppy Oil
This is a slow-drying medium, suitable for direct wet-into-wet painting methods, but should not be used when painting in layers.

Safflower Oil
This is used particularly for grinding white pigments. The same care should be taken regarding over painting as with poppy oil. A paint film with safflower white underpainting and overlaid colours in linseed oil could be unsound.

Cooked Oil
Although cooked oils were popular in the past, they are now considered unreliable and too yellow and are no longer widely used in painting.

A medium is either the same, or an additional mixture which may incorporate oil, turpentine and resin varnish, for instance.

There are many recipes for oil painting mediums which have been popular at different times. All have different qualities, but the safest method of oil painting remains that of using the tube colour as it comes, or simply dilute with turpentine, white spirit or oil or spike lavender.

Oil Varnishes


Cooked oil or resin varnishes were popular in the past. Preparation involved heating a hard fossil (like Baltic amber, copal, or the softer sandarac resin), with the drying oil, in a proportion of around three to one, which allowed the two to be incorporated into a thick varnish, like clear honey. The varnish had good film-forming characteristics and was strong, durable and glossy. The vernice liquida, as it was called, was a very dark reddish brown in colour. Cooked oil/resin varnishes are now not used for oil painting because of their dark colour.

Other types of oil varnish incorporated soft resins like mastic or pine resin in nut oil to produce a paler varnish vernice chiara which could be used with colours such as green or blue that would be adversely affected by the reddish tone of the vernice liquida. These varnishes still displayed a tendency to darken.