Oil, acrylic, watercolour, gouache and tempera explained
Every paint is coloured powder held in a binder. Learn how egg, oil, gum and polymer shape the look of a picture, and how to tell them apart.
A museum label that reads “oil on canvas” or “tempera on panel” is not just paperwork. It tells you how the painting was made, how it has aged and why it looks the way it does. Once you know the five great painting media, you start to see the difference from across the room. Here is a clear guide to what each one is, where it came from and what it means for the work on your wall.
Pigment plus binder, the basic recipe
Every paint has two main ingredients. The is the colour itself, a fine powder made from earths, minerals or synthetic compounds. The is the glue that holds the particles together and fixes them to the surface.
The binder decides almost everything: how fast the paint dries, whether it is glossy or matt, transparent or opaque, flexible or brittle. The same blue pigment looks quite different in egg yolk, linseed oil or gum arabic. The surface underneath, called the support, matters too, whether it is a wooden panel, canvas or paper.
Egg tempera, the medium before oil
For centuries, European painters bound their pigments with egg yolk. Tempera dries within minutes, so colours cannot be blended wet on the surface. Instead, painters build up form with many fine, hatched strokes laid side by side. A painters’ handbook written by Cennino Cennini around 1400 describes the method in detail.
Tempera was usually painted on wooden panels coated with , a smooth white ground of chalk or gypsum mixed with animal glue, often next to gold leaf. Sandro Botticelli’s The Birth of Venus, painted around 1485 and now in the Uffizi in Florence, is a famous tempera on canvas. The look is matt to softly satin, with clear, cool colours that have changed little over time.
Oil paint and its slow depth
Oil paint binds pigment in a drying oil, most often linseed oil. It does not dry by evaporation but by slowly reacting with oxygen in the air. Painters in the Netherlands refined the technique in the fifteenth century, with Jan van Eyck as its most celebrated master. The old legend that he invented oil painting is an oversimplification: oil had been used before, but he took it to a new level, as his Arnolfini Portrait of 1434 in the National Gallery, London, shows.
Because oil stays workable for a long time, colours can be blended softly. Thin, transparent layers called glazes let light pass through and bounce back, which gives old master paintings their inner glow. Paint can also be laid on thickly as , so that every brushstroke stands up from the surface. Over the following centuries canvas gradually replaced wooden panels as the usual support.
Oil is slow. A layer is usually touch dry within days but goes on hardening for months, which is why traditional varnish is applied only once the paint has fully cured. Linseed oil also yellows slightly with age, and many old oil paintings show a fine network of cracks known as .
Acrylic, the twentieth century newcomer
Acrylic paint binds pigment in a synthetic polymer emulsion. It thins with water while wet, then dries to a flexible, water resistant film. Mexican muralists experimented with synthetic resins in the 1930s, and water-based acrylic paints for artists reached the market in the 1950s. Many painters of the 1960s adopted them for large areas of clean, flat colour.
Acrylic dries in minutes, so artists can work fast and paint over a passage almost at once. It can imitate watercolour when diluted or oil when used thickly, although colours tend to dry slightly darker as the milky binder turns clear. The finished surface usually has an even, slightly synthetic sheen, and it does not yellow the way old oil does.
Watercolour and gouache, the water media
Watercolour combines pigment with gum arabic, a natural gum from acacia trees, and is diluted with water. It is transparent, so the white of the paper becomes the light in the picture. Even when dry, it can be lifted again with a damp brush. Albrecht Dürer’s Young Hare of 1502, painted in watercolour and gouache, belongs to the Albertina in Vienna and is shown only rarely because paper and pigment are so sensitive to light.
Gouache uses the same binder but far more pigment, sometimes with chalk or white added. The result is opaque, flat and velvety matt, ideal for crisp shapes, which is why illustrators and designers love it. Gouache can shift slightly in tone as it dries, and thick layers may crack because the dried gum is brittle.
How to recognise a medium, and what it means for care
Start with the label or the invoice: the medium comes first and the support second, as in “acrylic on canvas” or “gouache on paper”. Then train your eye with a few clues:
- Oil: depth and glow, soft transitions, visible ridges of paint, and in older works a fine web of cracks.
- Acrylic: even sheen, crisp edges and bright flat areas, rarely cracked.
- Tempera: matt surface, fine hatched strokes, often on wooden panel and sometimes with gold.
- Watercolour: transparent washes with the paper glowing through, and soft blooms where wet paint met wet paper.
- Gouache: flat, opaque colour with a chalky matt surface, usually on paper or board.
Care follows the medium. Oil and acrylic paintings on canvas usually hang without glass, away from radiators and direct sun. Watercolours and gouaches are works on paper and need protection: acid free mounts, UV filtering glazing and gentle light. When you buy, ask for the medium and support in writing, and ask whether an oil or acrylic painting has been varnished.
Terms in this article
- Binder
- The substance, such as egg yolk, linseed oil, gum arabic or acrylic polymer, that holds pigment particles together and fixes them to a surface.
- Pigment
- The finely ground coloured powder in paint, made from earths, minerals or synthetic compounds.
- Gesso
- A smooth white ground of chalk or gypsum with animal glue, traditionally used to prepare wooden panels for painting.
- Impasto
- Paint applied so thickly that brush or knife marks stand up from the surface.
- Craquelure
- The fine network of cracks that forms in the paint and varnish layers of older paintings as they age.
Readers ask
Can you tell oil from acrylic just by looking?
Often, but not always. Oil tends to have more depth, softer blends and, in older works, fine cracks, while acrylic has an even sheen and crisp edges. Modern painters can make each look like the other, so the label, the invoice or the artist’s own description is the reliable answer. A conservator can confirm the medium if it really matters.
Why are watercolours shown in dim rooms?
Watercolour and gouache sit on paper with very little binder to protect the pigment, so light can fade colours and yellow the paper over time. Museums therefore show works on paper at low light levels and for limited periods, then rest them in storage. At home, hang them away from direct sun and frame them with UV filtering glazing.
Do oil paintings need varnish?
Traditionally, yes. A varnish evens out the surface, saturates the colours and protects the paint from dust and grime, and it can be removed and renewed by a conservator. It is applied only after the paint has fully hardened, often many months after completion. Some contemporary painters choose not to varnish, so ask when you buy a recent work.
