Two of my favourite drawing tools are my Lamy Safari fountain pen and Platinum Carbon ink. I like this ink because it is very opaque, like Chinese calligraphy ink, it has body and has great presence on the paper. You don't get as much creep from the liquid being absorbed by the paper fibres. Thus, it scans well and is great for watercolour.
But this ink does have a dark side (sorry, the pun). It is robust – made with carbon powder, once it dries, it does not budge. Do not fill a pen with this ink unless you intend to use it on a daily basis. Regular cleaning is a must. Any leaks need to be cleaned up right away or your pen will be clogged for good.
Following the advice of Nina Johansson (who draws amazingly and it was on her blog where I first read about this ink), I fully clean my pen on every second filling, and will rinse the nib quickly under water if I suspect it is drying out.
One other tip I have discovered is to apply a bit of silicone grease at the weakest points. If any ink gets trapped, it will help prevent the pen from becoming glued together. In the diagram above, you can see that I apply it at the base of the nib where it slides onto the feed and where the converter fits into the pen barrel. I bought a small jar of silicone grease from Goulet Pens. It is quite inexpensive and a little goes a very long way.