Gouache (; French: [?wa?]), body color[a], opaque watercolor, or guache, is one type of watermedia, paint consisting of pigment, water, a binding agent (usually dextrin or gum arabic), and sometimes additional inert material. Gouache is designed to be used with opaque methods of painting. The term, derived from the Italian guazzo, also refers to paintings using this opaque method.
Gouache has a considerable history going back over 600 years. It is similar to watercolor because it can be rewet and the paint can become infused with its paper support. It can also form a superficial layer like acrylic or oil paint. Also like watercolor, gouache dries to a matte finish. It is similar to acrylic or oil paints in that it is normally used in an opaque painting style. Many manufacturers of watercolor paints also produce gouache and the two can easily be used together.
Gouache paint is similar to watercolor modified to make it opaque. Just as in watercolor, the binding agent has traditionally been gum arabic but since the late nineteenth century cheaper varieties use yellow dextrin. When the paint is sold as a paste, e.g. in tubes, the dextrin has usually been mixed with an equal volume of water. To improve the adhesive and hygroscopic qualities of the paint, as well as the flexibility of the rather brittle paint layer after drying, often propylene glycol is added. Gouache differs from watercolor in that the particles are typically larger, the ratio of pigment to binder is much higher, and an additional white filler such as chalk, a "body", may be part of the paint. This makes gouache heavier and more opaque, with greater reflective qualities.
Gouache generally dries to a different value than it appears when wet (lighter tones generally dry darker and darker tones tend to dry lighter), which can make it difficult to match colors over multiple painting sessions. Its quick coverage and total hiding power mean that gouache lends itself to more direct painting techniques than watercolor. "En plein air" paintings take advantage of this, as do the works of J. M. W. Turner.
Gouache is used most consistently by commercial artists for works such as posters, illustrations, comics, and for other design work. Most 20th-century animations used it to create an opaque color on a cel with watercolor paint used for the backgrounds. Using gouache as "poster paint" is desirable for its speed as the paint layer dries completely by the relatively quick evaporation of the water.
The use of gouache is not restricted to the basic opaque painting techniques using a brush and watercolor paper. It is often applied with an airbrush. As with all types of paint, gouache has been used on unusual surfaces from Braille paper to cardboard. A variation of traditional application is the method used in the gouaches découpées (cut collages) created by Henri Matisse. His Blue Nudes series is a good example of the technique.
"Guazzo", Italian for "mud", was originally a term applied to the early 16th century practice of applying oil paint over a tempera base, which could give a matted effect. In the 18th century in France, the term gouache was applied to opaque watermedia, although the technique is considerably older; it was employed as early as the 9th century in Persian miniature and had by the 14th century spread to Europe. During the eighteenth century gouache was often used in a mixed technique, for adding fine details in pastel paintings. Gouache was typically made by mixing water colours based on gum arabic with an opaque white pigment. In the nineteenth century, water colours began to be industrially produced in tubes and to boxes a "Chinese white" tube was added for this purpose. Later that century, for decorative uses "poster paint" was mass-produced, based on the much cheaper dextrin binder. It was sold in cans or as a powder to be mixed with water. The dextrin replaced older paint types based on hide glue or size. During the twentieth century, gouache began to be specially manufactured in tubes for more refined artistic purposes. Initially, gum arabic was used as a binder but soon cheaper brands were based on dextrin, as is most paint for children.
Interior, St Etienne du Mont, Paris, Charles Louis Lesaint. The Walters Art Museum.
A relatively new variation in the formula of the paint is acrylic gouache. Its highly concentrated pigment is similar to traditional gouache, but it is mixed with an acrylic-based binder, unlike traditional gouache that is tempered with gum arabic. It is water-soluble when wet and dries to a matte, opaque and water-resistant surface when dry. Acrylic gouache differs from acrylic paint because it contains additives to ensure the matte finish and the reworking time is slightly extended. Some brands can sometimes be removed or "lifted" for several hours after application, during their drying time.