Liquid watercolors are a good choice for airbrush use, liquid washes, and use with a pen. Some of these liquid watercolors were developed in the 1930s by a chemist named Ben Salis. He named his line of paints after his cousin, Dr. Ph. Martin. These paints have high-intensity color. Liquid watercolors can be brushed, sprayed, or dripped on the paper. They are sold in bottles with a dropper lid.