Frisket, also known as masking fluid, is used by watercolor artists to block out areas of the painting so they stay white. I always use an old, cheap brush when applying the masking fluid; it’s very sticky and tends to ruin brushes. You don’t have to apply a thick layer, though; a thin layer will produce the same results and dry a lot more quickly.

When the masking fluid is dry, it looks and feels a lot like rubber cement glue. Leave it on the paper, and it protects that area while you paint, even if you paint right over it. When your painting is dry, you can rub it off, and the paper will still white underneath.

I’ve tried a few brands of masking fluid, and the Incredible White Mask is my favorite so far. It has a milky-white appearance when first applied and turns yellowish color when it’s dry. It’s easy to use and easy to remove, and it protects the paper well. Because you don’t need much to cover an area, start with the smallest bottle available. I have yet to use up a whole bottle of masking fluid.