I’ve been preparing heavy watercolour paper by spongepainting, letting it dry, then drawing patterns with Wild Gears.
Watercolour paper stretches when wet, so needs to be taped down on a flat surface like a board. A better tape than what I’m using (beige masking tape or green painter’s tape) is gummed paper tape. You can buy artist’s tape or, apparently, the tape used by butchers. I need to get some, and perfect my stretching skills.
There are many other watercolour techniques to explore for creating beautiful backgrounds. Just do a search on YouTube.
Meanwhile, here are some videos of pieces that I’ve done: