Indian Ink used to be my favorite medium for the longest time in my childhood and Appa handmade the pens for me to use with the ink(which I still have and treasure) I recently discovered the ink pot sitting there incognito with my paints!
I used a wash with the ink for most of the painting of Radha and Krishna except for the finer details when I used my fine brush and the handmade pen-nib. It was interesting to note that I resisted the temptation to use a Sharpie. I have come to realise that 1. Sharpie drawings have this kind of metallic shine when viewed from an angle and 2. One cannot use a wash over a sharpie. 3. There is a charm in using Indian Ink! No it is not the same as Black Paint - acrylics or poster or oil :) You will know once you use it!
Radha is fetching water just as an excuse to see Krishna. For me, painting Him is just an excuse to experience Him also :)