Derwent Graphik Line Painter pens contain water-based pigment paint that is lightfast, opaque, waterproof and permanent. There are 20 vibrant colours in the range, all with a 0.5mm Japanese-made steel nib. The barrel is frosted so you can see the paint moving inside. When ink is wet, the paint is water-soluble however you only have about a 30 second window before it dries.