Experiment with Indian Ink

I've been trying an experiment.... this definitely works on absorbent watercolour paper, but does it work on a canvas board? I wanted to find out.
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.

When the gouache paint was absolutely dry, I covered the whole canvas with Indian ink, taking care to spread the black ink lightly so I didn't smear the gouache underneath. The canvas was a black rectangle, nothing else showing. Uhoh, what next?
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.

This was on plain untreated cheap canvas. Perhaps the ink might stick better if I had used some gesso.... maybe I'll try that next week.