Uni Posca Paint Markers use opaque, water-based ink rich in pigments, making them great for writing on nearly all surfaces: paper, glass, wood, metal, plastic, glossy surfaces such as photos, and more. The finished writing and markings have a matte finish on porous and nonporous surfaces. The ink can be scraped off of nonporous surfaces such as glass and acrylic, and are permanent on porous surfaces like wood and paper. The paint ink is waterproof, non-toxic, resistant to atmospheric conditions, and the colors are rich and vibrant. Posca markers work well for posters, sketching, drawing, lettering, and art-making. The pigment overlays perfectly on a variety of art mediums, such as acrylics, gouache or colored pencils. The pen body contains a small ball, and when you shake the pen before using, you can hear the ball rattling around and mixing the ink. The tips can be pulled out and turned over if worn, replaced with a new tip, or soaked in water if dried out. To start using the marker, first shake the pen, and push down on the tip a few times until the ink comes out. The Extra Fine marker produces a line approximately 0.7mm wide.