Dr. Ph. Martin's Pen-White is perfect for fine writing, and was made to be used in technical pens and airbrush. This liquid product delivers the same brightness and permanency of traditional watercolors in tubes, but is much more versatile and easy to use. It will also adhere to a variety of surfaces that include film and acetate-type material. The color is incredibly opaque and can cover dye and marker color. Ultra fine white ink (not waterproof). Flows through a 3x0 (0.25 mm) pen tip. Comes in a 1.0 oz (30ml) glass bottle with dropper.