Ink can be applied to a surface through a pen or by brush. Ink has been a reliable medium for many illustrators because of its permanence, versatility and its ability to be reproduced accurately.
Inks come in a variety of colors and can be applied to a variety of surfaces.
Mostly inks are applied to smooth surfaced papers, but watercolor paper is also an acceptable surface. Inks can be applied to dried watercolor paintings and are often used in conjunction other mediums.