The terms wet-on-dry and wet-on-wet do simply mean "wet paint applied onto dry paint" and "wet paint applied onto wet paint". It's important to know you've these two options, or watercolor techniques, as laying color on wet or dry paint produces very different effects.
Painting wet-on-dry produces sharp edges to shapes, whereas painting wet-on-wet the colors will spread into one another, producing soft edges and blending. Knowledge of these two techniques can also help prevent you from being frustrated by the paint not doing what you expect.
To try these essential watercolor techniques, you'll need the following:
- A piece of watercolor paper, ideally stretched on a drawing board so it doesn't distort.
- A brush of any size.
- Two different color paints.
- A jar of clean water.
- A cloth for wiping your brush.
If you want sharp edges to what you're painting, then any paint already put down on the paper must be dry before you paint another shape. If it is completely dry, then the shape will stay exactly as you'd painted it. If it isn't completely dry, the new layer will diffuse into the first (this is done deliberately when you're painting wet-on-wet).
Adding paint to a wet layer of paint on the paper produces a soft, diffused look as the colors mix. The extent to which the two colors mix depends on how wet the first layer still was and how dilute the second color was. You can get anything from a soft-edged shape to a widely spread pattern. In the example here, the blue was slightly damp when the red stripe was added, so the red hasn't mixed very far into the blue.
Being able to predict the results you're going to get working wet-on-wet takes practice, but as this technique can produce spectacular, lively paintings it's well worth experimenting with it. It's particularly useful for suggesting movement in a painting and for diffusing shapes when you don't want too much detail. Make up a file of your various attempts with notes on the colors you used (some pigments collect on the paper's surface, creating more of a texture than others), how dilute the second color you added was, how wet the first layer was, and what paper you used.
- If you paint a shape with clean water then paint a color on this, it'll run up to the edges of the shape. If you touch a brush loaded with color in the center of this shape, the color will flow into the moistened area, bleeding towards the edges.
- Don't stop with only two colors, use your colour mixing knowledge to create, for example, a sunset of deep purples, reds, and oranges by painting red, blue, and yellow wet-on-wet and letting the colors mix on the paper instead of premixing them on a palette. Get the colors you want to add ready before you start painting, plan where you're going to put them, then work fast so you get everything down before your painting's dried.