Have you ever used china markers/grease pencils in your artwork? They are oily so they work as a resist and I was just playing around with them (while the drywall mud dried in the bathroom today) drawing things in with them and then putting the watercolor on. You can see how it works in the blouse and the chair arm and the hair (a bit). I got 3 colors: crimson red/rouge cramoisi, white/blanc, and black/noir. The lips and flower were done with some of the red, too so there is a resist on them. I'm wondering how to best use these and just starting to use them and maybe figure them out. I wonder if you can dissolve them a bit with a turpentine wash or something similiar and how they'd look on Yupo paper...
I've seen Molly Brose use them over and over and her work is stunning - go to
to see her work which I love - each day she puts up something even better than the last day! She calls them grease pencils and makes some interesting textured pieces in her work. (I have the correct URL now - I left out a letter - you should be able to go to see her work now.)