For the gouache + ink technique, I took the angel statue photo and sketch and traced it onto a piece of 300# cold press watercolor paper (I think it's Arches but I use Arches and Fabriano interchangeably so could be Fabriano). It helps to have a heavier paper for this technique.
Using colored gouache as the "resist", and wanting greyed colors for the statue, I put out Winsor Newton Primary Red, Primary Yellow and Primary Blue on a large palette (so I could mix them, as needed), and filled in the lines with the three colors. (In this photo you see Burnt Sienna, as I originally thought I'd use it, too, but ended up with just the 3 primary colors.)
Painting with thick gouache right out of the tube (only wet your brush to get the gouache to move but don't think down the gouache), I brushed the colors on in all the areas I did not want white or black (remember the ink will show wherever you do not have gouache). If you want any area pure white, use white gouache to cover that before doing the next step! I did want white areas in the final painting, so got out some Winsor Newton white gouache and added it to those areas I had not covered with the primary mixes.
After the gouache dried (about 5 hours), I used an old household brush (pick up at any hardware store), and brushed on a single layer of black, waterproof, India ink and let that dry.
When the ink had dried, I was ready to wash everything off and see what I had. You can go outside and wash it all off using a garden hose, you can wash it off in the sink using and kitchen sprayer, or you can just wash it off by submerging it into a tub of water and gently brushing away the gouache and ink with the same household brush you used to apply the ink (make sure you washed that ink out well before you do this or you're just brushing ink around!).
When you have enough ink off the painting, you end up with something like this - which looks like a print. I left more of the ink on this one than in previous ones I'd done because I liked that it added to the rough texture of the statue and gave some dimension to the greenery in the background.
I first heard of this technique in a Val Webb online course. She used just white gouache and black ink and then painted in what she wanted with watercolor after everything was washed off and had dried. I liked that, but I searched around and found some artists using colored gouache and wanted to try it. It takes a bit more thinking when using colored gouache so you leave enough lines and spaces in the final covering (where the ink will settle). If you do get carried away and cover an area with gouache, you can always "cut" back into it with a sharp pencil to get back to the lines you covered.
What do you think? Ready to try it?
All you need are 4 tubes of gouache = yellow, blue, red, white; heavy watercolor paper or watercolor board, a bottle of waterproof (important that it's waterproof), black India Ink, a small brush for painting on the gouache, a rough household brush for painting on the India ink, a place where you can spray or brush off the dried gouache and ink and you have it!