Masking refers to temporarily protecting a specific portion of apainting to keep it from being covered by paint. Many watercoloristsuse masking fluid, or liquid frisket, which is a latex-based substancethat can be “painted” over areas that are meant to remain white. Whendry, frisket repels paint, so you can paint over it without coveringthe white support underneath. When the paint is dry, gently rub off thefrisket with your finger to reveal perfectly shaped areas of purewhite. Masking fluid is available in white and with tints. (The coloredversions are easier to see on white paper.)
STEP ONEFirst dampen an old brush and stroke it over a bar of soap to keep the bristles from absorbing too much fluid. Then dip the brush into frisket and apply it to areas of your painting that you want to keep white.
STEP TWOLet the frisket dry and then apply paint over it.
STEP THREEAfter the paint dries, rub off the frisket with your finger, revealing the white paper beneath. You can leave the area pure white or glaze over it to tone it down.