|Little dip pen|
Indian ink, drawn with the subject
I do quite a lot of ink sketches out and about with a Rotring Artpen (a cartridge pen), but dip pens (or "dippies" as I've started calling them) are not as practical; you need an open bottle of ink to hand, and in the conditions that I often sketch (standing in a wood or a field or on a footpath), I just don't have enough hands!
But dip pens do have their advantages. They can cope with far more ink types than any fountain or cartridge pen (the Rotring uses a modified Indian Ink that is less shiny and more watersoluble - full-on Indian ink, which is made from lamp-black, would clog the Artpen). They also have the potential to be more flexible. And greater flexibility, in a pen, means greater variation in line width (this is because a bendy pen's tines will move further apart under less pressure, and release a wider ink line). Which can permit some truly beautiful marks to be made.
I'm not saying that all of these marks are beautiful, but there are a few rather nice ones...
Quink (black and red) and water
Left: is simples; right: is wet