This Faber-Castell Pitt Artist Brush Pen Black allows you to draw with a lightfast, waterproof ink but without all the mess that usually involves.
The flexible brush point gives an even flow of brilliant, high-quality acid-free pigment ink that can be angled as you wish, and won't fall apart on you when you are in the middle of something.
Once you've tried a Faber-Castell Pitt Artist Brush Pen, you will want one close by at all times.