Gouache resist is a wonderful technique to achieve a painting with the air of a Lino print or wood cut. It will be quite illustrative, in that you often end up with a black outline. The unpredictability and rather messy process certainly appeals to me!
You will need gouache, waterproof ink, watercolour paper and watercolours.
First sketch your design. If you use hot press paper, you will get a more precise outcome. Your paper needs to be robust enough to be run under water, so use a decent quality one and I would suggest 140 lb in weight as a minimum. This little test is on Bockingford Not 140lb. Your lines can be bold as they will be covered with black ink in the final image.
Next paint all areas you do not want to be black. You can use white gouache and then use watercolours to paint at the end, or you can use coloured gouache. If you use coloured gouache much will be washed off and you will be left with a tint. So go bold at the painting stage. The consistency should be double cream. Too thin and the ink will seep through. You can thin with water if it is too thick. If you only have white gouache it can be tinted with watercolour, just don’t over thin it.
Hold your painting up to the light to see if you have missed anywhere. Or tint it very gently with ultramarine if you are only using white. It will help you see where you have painted. Let it dry thoroughly. And I mean THOROUGHLY.
Next the scary step. Black waterproof Indian ink is the traditional ink to use. Gently stroke the ink across your painting. Only one stroke per area to avoid lifting the gouache. Eek! Dry it thoroughly. The ink will soak in to the unprotected paper.
Now for the big reveal. Using cold water, wash your painting under a running tap or spray. The water loosens the gouache to show the image. You may need to gently scrub with a brush if any area doesn’t shift, but avoid too much scrubbing or your black will turn grey. The blotchy black areas are characteristic and add a charm (in my opinion). Now dry the piece or add further watercolour wet in wet, or wet on dry. I’d some ink has stuck in an unhelpful place you can use a scalpel or razor blade to shift it. Avoid cleaning things up too much – what’s the point?
I hope you enjoy this as much as I do. It’s a long process, but well worth the drama of the end result.