This is a beautiful, cool piece by Painter, Dianne Longson, watercolor 18 x 20. So ! Eraser-ism is also possible with watercolor. The trick is to paint diluted gum arabic on the paper first. This seals the paper and will allow scrape-outs using credit card fragments. I prefer scraping erasers with acrylic, credit cards with watercolor. Wear gloves, as your hands are directly in the paint.
Subsequently, Dianne asked me how large can it work: Here are my thoughts on this – If the gum arabic is used undiluted it seems to form a shiny, thick coating. This may crack or flake over time, especially when flexing and on larger sheets. I have not experimented, so I don’t really know. I guess you are blazing the trail. let me know how it works out.