Having the right brush is the key to making fine lines with watercolor.
Watercolors are an inexact medium to paint with; because you are often putting color onto the paper in large washes, you can't predict which way the paint will spread. But painting fine lines with watercolor is possible. All you need is a high-quality brush that's made for detail work, and to mix the paint in the proper proportion so that your brush picks up the pigment easily. It may take practice, but you can make fine lines with watercolor just as well as with oils or acrylics.
Instructions
1. Get the right brush for the job. Having a small brush is a start; paintbrushes are made in sizes down to #000 and smaller. Aside from the size, your paintbrush should also come to a point at its end. A round brush or a rigger brush is most useful for fine detail work.
2. Buy quality brushes. A brush's quality can be roughly estimated by its price. Many painters use sable brushes, but there are many quality synthetic brushes on the market. Good brushes are expensive, but they will last much longer and hold their shape better.
3. Mix your paint well. Even if you want to create very dark lines, you still need enough water for the paint to flow easily.
4. Paint on a dry surface. Wetting the surface beforehand is a useful technique for large washes, but fine lines are better painted on a dry surface so they won't bleed onto the rest of the paper.
5. Refill your brush often. The longer your brush's bristles are, the more pigment it will hold. You should refill the brush before the pigment starts running out, not after. This will help you make fine lines that are even and constant.
