An artist's grade latex paint is more expensive than a student grade - it has more pigment in it, which of course makes it more opaque. I often use a sponge to stipple rather than paint, just as ChickenHaunt said. The latex rubber mixture dries and will hide most imperfections from the brush or sponge. I always thought this was the best solution, as opposed to rubber cement, as it is the same material as the mask.