Professional Waterproof Technical Pens Filled With Rich, Black Ink! The Acurit Technical Waterproof Drawing pen is Perfect For permanent Application. Acid-free, lightfast rich black ink. Acurit Waterproof Pens are Ideal For projects that require exhaustive detail such as technical drawings and drafting, but can also be Used for more artistic endeavors such as Watercolor underdrawings. Each pen Features a convenient window on the side of the cap for nib identification. Are you looking for the next step in detailing your Watercolor artwork? Look no further, grab a single or 12-pack of your favorite nib Size for you or a gift to you artistic friends. Grab the Assorted nib Size 6-pack to test out Each nib Size to find your favorite!