Posca pens have loads of uses! They are permanent on porous (absorbent) surfaces and can be washed off smooth and hard (non-absorbent) surfaces. Here, we painted decoration on glass. When you become tired of it, simply wash off the decor and draw something new. Posca pens come in several different widths and are opaque, i.e., they can be used on dark surfaces. TIP! If you want to paint larger surfaces, you can squeeze out ink from the pen in the palette and paint with a brush instead.