Uni Posca paint markers use vivid, opaque ink that can write on virtually any surface, including paper, photos, glass, wood, plastic, and metal. The paint ink can be scraped off from nonporous surfaces like glass but adheres permanently to porous surfaces like paper. It shows up well on both light and dark surfaces, and once dry you can write over it with another Posca marker without smearing or showing through. The ink is water-based, non-toxic, lightfast, and waterproof.
To start using the marker, shake it with the cap on so that the ball inside rattles. Then uncap the pen, place the tip on a piece of scratch paper, and press down so that the tip is pushed back into the body of the pen. Press the tip down several times until the ink begins to flow.
This pen has a bold tip, which produces a line about 8 mm wide.