Uni Posca markers are famous for the ability to write or draw on any surface including paper, photos, plastic, metal, glass and wood. They feature vivid, 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. For the first-time use, please press down its tip back into the body of the marker. It may need to be pressed several times until the ink flows into the tip. Shake it with the cap on to make the ball inside rattles, which will increase the flow of the ink. The pen set contains 8 different sizes of Posca marker in black ink. The sizes include PCF-350 (brush tip), PC-1MR (ultra-fine bullet tip), PC-1M (extra-fine bullet tip), PC-3M (fine bullet tip), PC-5M (medium bullet tip), PC-7M (bold bullet tip), PC-8K (bold chisel tip), and PC-17K (broad chisel tip).