I'm playing with my long lost Rapidograph technical pen set and Doc Martin's Bombay White india ink! The first test was an ATC with a mini-mandala on watercolor.
These doodles were drawin with a Rapidograph .8mm nib on a paper pad cover. The original is on the brown cover of a paper pad morphed into magenta digitally.
The white ink is versatile; it creates an imperfect and unique line with subtle shading.