• David Cox, 'Tour d'Horloge, Rouen' 1829
    David Cox
    Tour d'Horloge, Rouen 1829
    Pencil and watercolour on paper
    support: 343 x 257 mm
    Presented by the Art Fund (Herbert Powell Bequest) 1967

Watercolour is produced by mixing powdered pigments with a water-soluble gum, such as gum arabic, a natural secretion from acacia trees. The gum ensures that the pigment spreads evenly through the water, rather than settling or gathering in lumps. It also makes the pigment stick to the paper once the water has evaporated. Watercolour is transparent, so that the white of the paper remains visible through strokes and washes of colour, giving them a freshness highly valued by artists, especially for landscape painting. Like lithography, the technique was particularly associated with British artists.