Although traditionally done with ink or acrylic paint, it can be done with watercolours also.
This can be done with stamps and stencils, with wet or dry paper, and augmented afterwards with other materials such as coloured pencils or pens.
If stamping, for example, cover the stamp with wet paint and stamp it on your surface. If you do this on a dry surface, the image won't bleed, but if on a wet surface it will.
This process can be used to create, for example, offset images if you draw onto them after they're dry.
