Spray pen refers to a tool that looks like an oversized fountain pen. It has a container that can hold up to one ounce of liquid pigment and a thin tube that connects compressed air and carbonized gas source. Pen-spraying can produce uniform colors and hierarchical effects of colors. This is an exquisite version of the SPRY gun. Pen-spraying technique is usually different from writing brush technique, and it is more favored by commercial painters than pure artists.