First I used water soluble blue gouache paint to sketch out a negative image on a cheap 4" x 6" canvas board from the Dollar store. I didn't want to waste a bigger more expensive canvas. Everywhere I wanted the canvas to stay white I painted with the gouache.
Then when the Indian ink was completely dry, it's time for the experiment. I held the canvas under the tap and scrubbed gently with a soft paintbrush. When the gouache started to soften in the water, it washed off the canvas taking the ink with it, and leaving black ink where there was no paint.
I may have rubbed too enthusiastically as some of the ink came off the canvas too.
So I darkened some of the greyed out lines with more ink and added a light colour wash of ink and gouache paint. It doesn't look too bad. Sort of what I intended.