Art - Oil Paint
Oil paint was originally developed as a substitute for egg tempera, which only dried in direct heat or sunlight and therefore prone to cracking. Combining several different ingredients creates oil paint, as we know it, although it is now quite common for artists to buy pre-prepared tubes, which they then adapt to their needs.
Oil paint consists of pigment blended with oils ('binders') that oxidize upon contact with air, forming a 'skin' that disperses the pigment evenly. As gas forms beneath this 'skin', it pushes its way to the surface, which allows air to the layers beneath. This process is ongoing until the 'skin' is totally dry.
Each layer must be completely dry before the next can be applied, and each of the subsequent layers mix must contain more oil than the previous one. The layer beneath absorbs the excess oil, which is a process known as 'fat over lean'. Depending on the amounts of thinning agent and oil used it is possible to achieve many different levels of viscosity.
The most commonly used oils are linseed or poppy. Linseed oil is made by steaming the flax before pressing the seeds, while poppy oil is derived from the opium poppy. Linseed oil is quite poor quality and can be dark in colour. On the other hand poppy oil is an excellent binder for whites and pale colours. However it dries slowly and is prone to cracking.
Solvents are added to the mixture to adapt the consistency. The most popular of these would be turpentine, which is derived from gum trees, and white spirit. However although white spirit is long lasting, it is also quite odorous. A suitable solvent must evaporate evenly and should not react with any other element in the mixture.
Varnish can be used as a binder to create glazes, and also as a protective film over the surface of the finished piece.
It is vital to apply a coat of varnish over a piece if dryers have been used to facilitate the drying process. Dryers are metallic salts that are blended with the oil paint mixture before it is painted on whichever surface the artist favours. However these salts may affect the permanence of the piece.
Oil paint can be used on a multitude of surfaces- wood, paper, cardboard, canvases and even sheet metal. The most popular would be some form of canvas. The term canvas applies to any fabric stretched over a frame, almost always wooden. Linen and linen weaves, cotton and cotton weaves e.g. bleached calico, mixed linen- cotton weaves e.g. Hessian and even man- made fibres are all examples. Linen is considered the best quality due to its fine weave and smooth surface.
Any surface, except metal that oil paint is to be applied to must initially be primed to ensure the painting fully adheres. On canvas these 'grounds' act as a shield between the fabric and the oil that, if left untreated, would eventually rot the material. Most grounds are white to combat discolouration, and are generally made up of a combination of terps or white spirit and linseed oil.
Oil artists may use a wide variety of tools such as hog hair and sable brushes, palette knives, pieces of card and even their fingers to create an image. A huge variety of different marks and texture can be obtained. Most artists who work in oils will generally start with an under-drawing or under-painting to use as a guide.
Oil painting could be considered one of the most popular artistic methods, both in a historical and contemporary context. Its advantages mean that a piece can be worked on over several months, and built up in layers at the artist's own pace.