Tried scratching the outlines of a whole picture into a piece of A3 paper with a stanley knife. Difficult because I couldn’t see what I had done. Then I painted over the whole sheet of paper and the lines individually hoping to fill the channels with watercolour.
Only limited success. The lines don’t stand out as much as they do in the little flower drawing, but still works in principle. Plus gave me a very free drawing because it has been defined by marks that I couldn’t easily see as I was making them.