The overwhelming majority of paintings shown in articles here are made using oil paints on canvas, although some use wooden panels or copper plates instead. In this series of articles, I’m going to survey the different media used in painting, not just from a technical sense, but how choice of media influences the painting that we see.
Over the millenia that humans have been painting as art (in its broadest sense), we have used a very wide range of methods for putting colour on different surfaces.
Earliest surviving paintings, such as these from around thirty-six millenia ago, in the Chauvet-Pont d’Arc Cave in the Ardèche, were simple applications of pigment to a stone surface.
A modern painting made using acrylics on canvas has come a very long way, but the underlying principles remain unchanged. As an introduction to the terminology used, let me explain how painting media work so as to make clear the terms I use throughout this series.
Although there’s no reason that you can’t paint three-dimensional surfaces and call that a painting (and many artists have done so), I will make an artificial distinction here that such 3D objects are sculpture. There’s a very long history of polychrome sculpture which precedes radical works of the twentieth century. So what I define here as a painting is the application of colour to an essentially flat surface.
By convention, the surface on which paint is applied is assigned two named roles: as the physical support for the painting, a purely mechanical task, and to provide the ground on which the colour is applied. Those roles are distinct, even when a single surface such as a wall or sheet or paper fulfils both. In this series, we will look at a range of supports from the walls of buildings, which are rigid, massive and immobile, to fragile sheets of paper.
Most traditional paintings by professional painters made in the last few centuries have been on supports of stretched canvas, which have been sized to protect their fibres, then had a white or tinted ground such as chalk bound to them.
Support and ground form the receiver, on which colour in the form of pigments have to be bound. Although it’s possible to get pigment to adhere to a suitably rough ground – which is part of the principle behind painting in pastels – the result isn’t very durable, and clients and patrons are likely to be wary about paying for a painting which literally crumbles into dust in front of their eyes.
Not all paints contain pigments: some prefer soluble dyes instead. Generally dyes, which have often been derived from plants, aren’t as durable. Pigments consist of large insoluble particles, as seen in the cross-section above, which protects them from physical damage, chemical reactions, and most importantly the adverse effects of exposure to light, which can cause their intensity to fade.
The goal of many paint systems is to trap these pigment particles in a solid layer formed by a chemical binder which is liquid when applied but hardens by the chemical process of polymerisation into a solid. In the case of oil paints, the binder is an oil which undergoes slow oxidation to form the polymer – a drying oil, such as linseed oil, obtained from the common flax plant.
The final component involved in a painting is one which should vanish during the process of applying the paint: a diluent or solvent which is used to thin the paint, and clean wet paint from brushes and the other tools used in the process. Diluents are often confused with binders, but usually they are opposites: an ideal diluent should evaporate quickly, leaving no residues and a robust if thin paint layer behind for the binder to turn it into a strong, enduring and faithful record of what the artist intended.
In traditional oil painting, typical diluents are organic solvents such as turpentine and white spirit, which are used to spread thinly the layer of drying oil binder and pigment particles. Remove most of the drying oil and use largely diluent, though, as in peinture à l’essence, used by Degas, and you can end up without any proper paint layer at all, with powdery pigment trying not to fall off.
In this respect, watercolours are strangely named. Oil paints rely on drying oils as their binder, but in watercolours the water is the diluent, not the binder, which is actually gum arabic; many other painting methods also rely on water as diluent, but aren’t called watercolour because of that.
Support, ground, pigment, binder and diluent: those are the key components in most painting systems, which I will discuss in the articles in this series.