To choose a watercolor technique, first consider what sort of edge the shape requires. If the paint should flow and blend to create soft edges, wet-on-wet is likely your best option. But if you need a clearly defined shape, wet-on-dry allows for greater control. Neither technique is superior; they behave differently because the presence or absence of water on the paper dictates how far the paint is able to move.
With wet-on-wet, clean water is added to the watercolor paper before paint. The paper should not have deep puddles of water but be evenly damp. When a brush full of paint touches the wet paper, the pigment begins to move away from the edge of the brush. On wet paper, the pigment spreads further and creates a softer edge. Damp paper produces less spreading. Wet-on-wet is appropriate for soft backgrounds, blended color areas, soft shadows, skies, and any other area where you don’t want all the edges to appear sharp.
Wet-on-dry involves placing wet paint on dry paper. Because there’s no excess water to push the pigment outwards, the edge remains close to where the brush was applied. It’s suitable for crisp silhouettes, small shapes, hard edges, controlled washes, and secondary details. It’s also easier to use when you’re trying to protect a thin highlight or paint carefully around a different shape. The amount of water in the brush still matters: a heavily loaded brush can leave a thick line of pigment or spill over its intended boundary even when the paper starts out dry.
It’s helpful to compare the two techniques with the same shape rather than practicing each one as an independent exercise. Lightly draw a few leaf shapes on watercolor paper. Paint one leaf on dry paper and watch how closely the pigment follows the edge of the brush. Then, wet the shape with clean water and, once the water has formed an even sheen across the shape, bring pigment to the paper. Finally, on another leaf, let the wet paper get slightly damp before adding pigment. You’ll notice how much the pigment moves on the three leaves even though the paint and the shape are the same. This provides a good comparison of how paper moisture relates to edge quality.
Sometimes, problems occur when the technique shifts mid-painting. You might begin a wet-on-wet wash, pause to adjust the wet paint, and then return to the painting once part of the paper has started to dry. You could end up with pigment meeting a partially damp surface and creating blooms or backruns or unanticipated hard edges. Or you might attempt a wet-on-dry application but end up flooding the paper because you’ve overloaded your brush with water. Keep an eye on the paper’s sheen just as much as you remember which technique you’re using.
Watercolor paintings frequently use both techniques. A large wet-on-wet area can be allowed to dry and then shaped or glazed with wet-on-dry paint. You can also dampen only one side of a wet-on-dry shape to create a combination of hard and soft edges. When figuring out what to do next, think about your subject instead of sticking to one technique throughout. Does the edge of this shape need to spread or stay defined? This question provides a practical rationale for deciding whether to use wet-on-wet or wet-on-dry.
