Making Green: Tempera versus Oil | National Gallery, London

The appearance of a painted colour depends partly on the pigment, but also on the ingredients used to bind the paint together. Pigments mixed with oil produce a glossy finish. Pigments mixed with egg yolk, to make egg tempera paint, will have a flatter, matt appearance. Pigments made from mineral clays, known as green earths, bound in egg tempera, were used by Italian artists from the 13-15th centuries as a base colour for flesh. These greens were used to suggest shadows, and model the shape of the face. Pinks, reds and white highlights were added on top. Tempera dries so quickly, that different colours can't be easily blended on the painting surface. So artists used delicate hatching when applying the different colours. The very green skin tone of many Renaissance faces may be due to the layers of pink paint having faded, revealing more of the base layer than was intended. With oil paint, the pigment is bound in certain kinds of oil, often linseed or walnut, that dry to form a tough film. Jan van Eyck was particularly famous for his skill at working in oil. Oil paint dries slowly and so can be manipulated on the picture surface. Some pigments are opaque, others can be used to make a translucent 'glaze'. Glazes can be built up in layers to produce a deep, glossy colour that can imitate gleaming satins, costly wool, velvet and rich silk damask.