Spattering can add spontaneity to a watercolor or acrylic painting if done correctly and with reserve. And it’s quite simple to do. Some artists prefer the toothbrush method where you run a finger over a toothbrush “charged” (loaded) with paint. But I prefer to tap or hit a charged brush against another brush. This gives me more control over the size and amount of spatter. It’s also possible to give the spatter direction by tapping the loaded brush at an angle.
In the first stages of developing a painting, I often spatter to break up large areas and to create texture and interest in the background. Even though most of this gets lost by the time the painting is finished, it gives the underpainting subtle variations. I also use spattering to create interest on rocks, ground and walls. Dark areas that have become dull and uninteresting can be revived by spattering and then lifting off color with a tissue or sponge.