Uni Posca markers are famous for the ability to write or draw on any surface including paper, photos, plastic, metal, glass and wood. This pen set features opaque ink which is water-based, lightfast, waterproof and non-toxic. The ink is removable on nonporous surfaces like glass but will be permanent on porous surfaces like paper. They show up well on both light and dark surfaces. After drying, you can cover it with another Posca marker without any problems. Uni Posca PC-3M marker features a 1.8 mm bullet nib.