Paint = pigment + binder
Every kind of paint has the same two parts:
- Pigment: a fine coloured powder, from minerals, plants or made in a factory.
- Binder: a sticky liquid that holds the pigment and attaches it to the surface.
Some paints also have a thinner (water or oil) to make them flow. The binder gives the paint its character: how fast it dries, how shiny it is, whether it can be washed off and whether it covers what is under it (opaque) or lets it show through (transparent).
Watercolour, oil and Japanese-style (nihonga) painting have their own lessons. Here we look at other common media.
Acrylic
Acrylic paint uses a plastic polymer as its binder, mixed with water. It dries in minutes when the water evaporates and leaves a flexible plastic film that is water-resistant. You can use it thin like watercolour or thick like oil. It sticks to canvas, paper, wood, cloth and walls. Wash your brush before it dries!
Tempera and gouache
Tempera uses egg yolk as binder. Before oil paint became common, artists in many places painted wooden panels with egg tempera. It dries quickly to a smooth, matte and long-lasting layer. Because it dries fast, the artist builds colour with many thin strokes and layers (hatching). Some wall paintings, including many old paintings in Indian caves and temples, are described as tempera-like methods on prepared plaster.
Gouache (say "gwash") is like watercolour, but it has white chalk-like filler and gum binder. It is opaque, dries flat and matte, and can be re-wetted. It is loved by illustrators and for posters and school art.
Ink wash (sumi-e)
In East Asia, painters use black ink made from soot and glue. A stick of ink is rubbed on an inkstone with water. The brush is dipped in thick or watery ink. The same ink gives many greys: less water is dark, more water is light. One stroke can even have a dark tip and a light tail. Ink wash is painted on absorbent paper or silk and teaches control, because ink cannot be erased. Painters leave empty paper on purpose to suggest mist, water or sky.
Fresco and wall painting
Fresco (Italian for "fresh") is painted on wet lime plaster with pigments mixed in water. As the plaster dries it forms a hard crust that locks the pigment inside. The colour becomes part of the wall and can last for hundreds of years. Because plaster dries in hours, the painter plasters a small patch each day and paints it quickly. Painting on dry plaster (secco) with a binder like egg or glue is another wall method. Other media you may meet are pastel (pigment sticks), encaustic (pigment in hot wax) and mixed media (combining several).
Key formulas and definitions
- Paint = pigment (colour) + binder (holds it) [+ thinner]
- Acrylic = pigment + plastic polymer; dries water-resistant
- Tempera = pigment + egg yolk; matte, thin layers
- Gouache = opaque watercolour with chalky filler; matte, re-wettable
- Ink wash: more water = lighter tone
- Fresco = pigment in water on wet lime plaster; colour locks in as it dries
Worked examples
1. Why does a thick acrylic stroke hide the black line but a watery ink stroke does not?
Thick acrylic has a lot of pigment in every layer, so it is opaque. Watery ink spreads the pigment thin, so the black line shows through.
2. A fresco artist paints a wall in sections, not all at once. Why?
Plaster dries in a few hours and colour must go on while it is wet, so only a patch that can be finished that day is plastered.
3. Which medium would you choose for a quick poster that needs flat, bold colour, and why?
Gouache, because it is opaque, dries flat and matte, and is easy to use with water.
Common mistakes
- Thinking pigment alone is paint. Without a binder it does not stick.
- Using acrylic and letting it dry in the brush. It will not wash out.
- Adding too much water to ink and thinking the paint is "weak". It is just lighter on purpose.
- Trying to fix fresco after the plaster has dried. It is very hard to change.