This was one of those "learn something new today" facts that came across while reading Mastering the Watercolor Wash by Joe Garcia to my art therapy client.
Joe Gracia claims that once you understand the process of how to do these washes, the world of watercolor painting opens up to you. The four washes are: flat, gradated, wet-into-wet and streaked. Painting each one requires a slightly different approach.
The flat wash looks like the name implies. There is no gradation from top to bottom or side to side. It has one value. This is a great wash for skies or buildings where a flat value is needed.
A gradated wash is one that gets progressively lighter in value. The gradated wash starts with the desired color and value and more water is added as the wash continues. It is a great wash for landscapes where mountains fade into the mist or dark rich skies fade into the horizon.
The wet-into-wet technique is the wash most often used. Colors are placed side by side on a wet surface and allowed to flow together. Soft blending is the result of this wash. Because of the wet surface there is less control. It is a great wash for controlled accidents.
The streaked wash is really a tool to get you to think about washes and texture. The color is placed on a wet surface, then you pick up your drawing board and tilt it in the direction you want the texture to run. This technique is good for showing the wind blowing the clouds or rain.
There are no rules on how washes should be done. It is up to the artist to make them work. Joe believes that practice is the key to success.