In watercolor, one of the most valuable tools is a brush with no paint on it. By saving whites — large, or small highlights — you can make the painting seem to glow from within, rather than just shine off the surface. A lighted and airy effect is something that you can only get quickly with this medium. New watercolorists will instinctively want to fill up the whole sheet. The very best watercolors, however, are often about what has been left out. Learning to leave well enough alone is a positive skill that will develop as you go.
In order to keep whites, you have to plan ahead and hold off, right from the start of the painting. You have to be able to mark in the places of highlights, the bright edges of clouds, the spray on the surf, the shine on the wet rocks, before you lay the first wash on the paper. You use masking fluid, or you gently dry-brush around the places you want to save, or you simply and bravely paint around them. All of these methods preserve the white paper, and if done successfully, that white appears to shine in contrast to whatever colors surround it, and it gives a shape to what is present without your laboriously drawing it for the viewer. And all of it looks easy, even though it takes planning and a steady hand.
To maximize the illusion of atmosphere, white space needs to cooperate with soft edges and gradual washes. In a landscape, a mountain seems further away if its bottom edge is softened with mist, and its top edge sharpens in sunlight. In a street scene, a person in the distance seems more real if surrounded by soft, diffused color and illuminated by a single sharp highlight on the shoulder. The interplay between light and dark, hard and soft, creates atmosphere and mood that simply cannot be achieved with flat value. As you paint, you will come to have an intuitive sense of where the light likes to land on the paper, and you will use white to create mood and direct the eye.
Allowing white space to remain in your painting also helps you learn about one of the most powerful attributes of watercolor: economy of means. One highlight can convey the feeling of a sunny day; a thin stripe of unpainted paper can evoke the presence of water without your needing to describe every wave. In addition, using white space sparingly helps you focus on what is most important in a scene rather than on every detail. Many artists report that their best paintings are the ones in which they avoided over-working them and allowed the white paper to provide the needed content, giving the painting a fresh and life-filled appearance.
Finally, the ability to leave white space effectively means that watercolor painting shifts from an additive technique to a subtractive one: Every bit of white space left in the painting is a space for the viewer to breathe; a space where light can pass through, where life can flow. And for the artist who is willing to “stop and smell the roses” — to not paint in every spot — the resulting painting will feel as refreshing to the viewer as the moment was to the artist.