Chemistry of Colour

Chemistry is the study of the composition, structure, properties and behavior of a substance, such as pigments (a powdered substance) found in paint. Thanks to the discovery of new chemicals in the nineteenth century, such as coal tar used to make mauve, the French Impressionists could experiment extensively with colour contrasts by using synthetic paints. Pre-mixed synthetic colours, such as magenta and arsenic-based emerald green, replaced prior methods of mixing primary colours. As painting landscapes outdoors or en plein air was favoured by the Impressionists, emerald green was a much-loved hue due to its vivid appearance.

What is paint?

A natural pigment is a powder which has been used by grounding materials such as clay and minerals. These pigments are usually mixed with a binder and/or a medium, such as animal fat or plant extract, which then makes the paint wet and holds the pigment together. A synthetic pigment is made artificially and may be either chemically identical to the original pigment, or a new chemical all together.

Modern paint is a mixture of pigment, binding medium and solvent. The binder is a liquid polymer that hardens to form a continuous layer when paint dries, while the solvent dissolves the binding medium to make the paint more fluid.

Historically artists used paint created with only a pigment and a medium (such as oil). However, since the invention of solvents, modern paints are easier to work with as they don’t dry as quickly so you can work them more easily, and they last longer.

Binding mediums (or binders) come in different types. For modern oil paints a binder may consist of a drying oil, most commonly linseed oil. In water- based paint a popular binder is poly vinyl acetate (PVA). The binding process gives the paint the texture we are all familiar with.

However, to make paint easier to work with on a surface and extend its volume, some artists use a solvent or medium to thin the paint. The solvent for water-based paint is water, used in acrylic paints or watercolours. In oil-based paints the thinners are an oil based solvent such as Flow Medium, odourless solvent, Oxide Patina or Turpentine.

Natural

For thousands of years Aboriginal people have been blending science with art by creating paint and developing techniques, combining these to tell their stories. Historically, the most common colours to be found on rock and bark paintings consisted of red, white, yellow and black. These colours are found to naturally occur in the Australian environment. For example, Kaolinite is a soft white clay and can be found in most parts of Australia, while areas between Uluru and the South Australian border are unique for their metallic red pigment. These pigments are then mixed with natural binders such as egg yolk, kangaroo blood, bush honey or tree resin. The survival of ancient rock and bark paintings are dependent on the conditions in which they exist today and can be affected by climate, location and exposure to the impacts of the tourism industry.

Synthetic

Today, oil paint is made by mixing a synthetic pigment with oil and consequently this can take a long time to dry. Artists such as Ben Quilty use large quantities of oil paint mixed with gel medium to make the paint thick and lusciously textural.

Did you know?

Emerald green was highly toxic and was used as a pesticide to kill rats in the sewers of Paris, as well as pigment for paint!