Watercolor (US) or watercolor (UK), also aquarelle from French, is a painting method. A watercolor is the medium or the resultant artwork, in which the paints are made of pigments suspended in a water soluble vehicle. The traditional and most common support for watercolor paintings is paper; other supports include papyrus, bark papers, plastics, vellum or leather, fabric, wood, and canvas.
Watercolor painting has the reputation of being quite demanding; it is more accurate to say that watercolor techniques are unique to watercolor. Unlike oil or acrylic painting, where the paints fundamentally stay where they are put and dry more or less in the form they are applied, water is an active and complex partner in the watercolor painting process, changing both the absorbency and shape of the paper when it is wet and the outlines and appearance of the paint as it dries.
Many difficulties occur because watercolor paints do not have high hiding power, so previous efforts cannot simply be painted over; and the paper support is both absorbent and delicate, so the paints cannot simply be scraped off, like oil paint from a canvas, but must be laboriously lifted by rewetting and blotting. This often induces in student painters a pronounced and inhibiting anxiety about making an irreversible mistake.
Watercolor has a longstanding association with drawing or impression, and the common procedure to curtail such mistakes is to make a precise, faint outline drawing in pencil of the subject to be painted, to use small brushes, and to paint limited areas of the painting only after all adjacent paint areas have completely dried.
Another characteristic of watercolor paints is that the carbohydrate binder is only a small proportion of the raw paint volume, and much of the binder is drawn between the hydrophilic cellulose fibers of wet paper as the paint dries.
As a result, watercolor paints do not form an enclosing layer of vehicle around the pigment particles and a continuous film of dried vehicle over the painting support, but leave pigment particles scattered and stranded like tiny grains of sand on the paper. This increases the scattering of light from the pigment and paper surfaces, causing characteristic whitening or lightening of the paint color as it dries. The exposed pigment particles are also naked to damaging ultraviolet light, which can compromise pigment permanency.
Watercolor paint is traditionally and still commonly applied with brushes, but modern painters have experimented with many other implements, particularly sprayers, scrapers, sponges or sticks, and have combined watercolors with pencil, charcoal, crayon, chalk, ink, engraving, monotype, lithography and collage, or with acrylic paint.
Many watercolor painters, perhaps uniquely among all modern visual artists, still adhere to prejudices dating from the 19th century rivalry between "transparent" and body color painters. Among these are injunctions never to use white paint, never to use black paint, only to use transparent color, or only to work with "primary" color mixtures. In fact, many superb paintings flout some or all of these guidelines, and they have little relevance to modern painting practice.