Watercolor vs. Gouache: A Review of Differences and Creative Limitations
By Rick Jones
One of the questions people coming into our store ask frequently is “What is the difference between watercolor and gouache?” They assume that since both are water soluble, watercolor and gouache are the same. Some think that maybe gouache is just another fancy name for acrylics since they, too, are water soluble. But not so.
Well, as with all paint, the pigments are pretty much the same. Where they all differ is with the stuff that holds the pigment together—the binder. From a chemical standpoint, that’s where the magic lies. The binder in watercolors, which is a weak substance called gum arabic, is easily broken down by water whether the paint is in tubes or pans. Gum arabic and small amounts of water create pigment application that is transparent. Rather than using white paint to make lighter colors, the white of the paper serves this role. Since the white shows through the thin layers of pigment, watercolor tends to be airy and luminous at the hand of an experienced watercolorist. The trick to achieving this rich and luminous quality is to use very little water. In fact, there is a faction of watercolor artists who have challenged themselves over the years to use no more than a shot glass of water with each painting they complete. They refer to themselves as the “Whiskey School” of watercolorists. At the same time that learning the power of the white paper and how to use it by the delicate application of watercolors can determine the luminosity of these paintings, the challenge with gouache is keeping the application of that paint from becoming boring and flat. One final note on watercolors, good quality paints have the finest pigments ground to a very fine consistency so washes can be spread without leaving a grainy effect when dry. Gouache goes on a bit more like house paint.
The same pigments, although not as finely ground, go into the making of gouache (pronounced “gwash”). This paint is essentially opaque watercolors. Where gum arabic is the primary binder in watercolors, better quality designer’s gouache can have a number of ingredients. These may include preservatives, wetting agents, distilled water, titanium dioxide, gum arabic, and plasticizers in addition to dry pigment. Since gouache contains more binder than pigment, they go on velvety and smooth and the titanium dioxide gives them their opaque quality where watercolors are thin and much more fluid. Gouache goes on in an opaque film. The titanium dioxide, or sometimes zinc oxide (also found in UV blocking products like sunscreen), gives gouache that characteristic chalky and matte finish. Some artists and designers prefer that matte opacity and the blendability of gouache. If applied too thickly, it does have a tendency to crack. These are two of the more difficult mediums to master. Heavy paper of at least 140# is best since both require water and lighter papers can buckle or warp. Taping the edges with a gummed tape can keep the paper stretched as it dries as most watercolorists know.
Gouache lends itself to mixing and a talented artist in the medium can achieve remarkably luminous surface colors. Find quality gouache in better art supply stores and give it a try. The better the quality, the better the results.