Thomas, here’s something that I do on occasion when I’ve overworked the paper to the point that it would take color anymore, and I feel the painting is ruined. I use Sakura metallic and moondust gelly roll pens over the watercolor. It adds shine to the dull look that has occurred. I get more compliments on these ‘saves’ then I do on almost any of my other paintings.
It’s more for fun, though, because I don’t think gel pens are lightfast, but you can get some cool effects. The photo is already in the gallery so I’ve just posted the link here: