Use these removable fluids to make specific areas water resistant. They will retain areas of white paper or areas of underpainting, then easily rub off with a finger or eraser. The handy dispensing bottle allows for fine detail work. - Schmincke Aqua Masking Fluid - Colorless, 19 ml BottleSchmincke Aqua Medium, MASKING FLUID 19ML - This removable, colorless fluid makes specific fields water resistant. It will retain areas of white paper or areas of underpainting that you want to reserve, and then can easily be rubbed off with finger or eraser. The handy dispensing bottle allows for fine detail work. Allow masking fluid to dry thoroughly before painting and do not leave masking fluid longer than two days on the paper. It is also recommended for airbrush use.