When painting a watercolor, it is important to plan your white spaces ahead of time. These areas will be left white; the white of the watercolor paper. Unlike oil painting, where the whites are added at the end, watercolor requires the artist to plan ahead and “save” them from the start. Often, large white areas can be painted around, thus preserving the white of the paper. This becomes more difficult with smaller areas.
At times “saving” your whites isn’t easy to do. For instance if painting a white bird in the sky, it is nearly impossible to paint around the bird and have the sky look natural. Often times the sky is painted with layers of washes going horizontally across the paper. This makes it very difficult to “save” the small area of white for the bird. This is where masking fluid comes in to play. It is applied to the paper to block out this area, and painted over. I suggest practicing before applying the masking fluid to your painting so you will be familiar with its qualities.
An important tip when using masking fluid is to first wet your brush, then coat it with soap. (preferably from a bar. I keep a bar of soap with my painting supplies for this purpose.) Without the soap, the masking fluid will adhere to the bristles of the brush and ruin it! After coating the brush with soap, dip it in the masking fluid. Now carefully cover the area you would like to preserve as white. Don’t dip your brush back into the fluid without repeating the addition of soap to the bristles. Once you are satisfied that your area is totally covered, let it dry completely!
Once dry, you can paint your masked area. After your paint has dried the piece of masking fluid can be rubbed off with your finger or an eraser, revealing the white of the paper. At times, you may not be pleased with the result. The edges may not be as crisp as you intended, or the shape may not be quite right. This is why it is important to apply the masking fluid with great care. Even so, the result may lack the precision needed.
A word about masking products: In addition to white, masking fluids now come in colors as well. Some include an applicator or brush, and fine point tips are also available. There are translucent masking fluids, which allow you to see through to your paper, giving you a more complete look at what has been masked.
Experiment with this watercolor tool. You will soon decide whether or not you want to include it with your watercolor supplies.