2 X Uni Posca Aqueous fine PC-3M Black - Regardless of the color of the groundwork, it develops vividly. Once dry, you can overwrite. The ink color underneath does not show through.You can write on various materials such as plastic, metal, glass, photographs, mirrors, and wood. It has excellent lightfastness and does not flow with water when dry. Since it is water-based ink, it does not have an unpleasant smell and can be used safely by children.