I like this method of working, it produces random effects which can look very effective. I read about the method in a mag article and decided to give it a go, it works so I would like to share it with others.
I use watercolor paper, gouache paint and black ink. first create your painting using the gouache paint. paint all parts that need to be coloured including painting all white parts white - anything not covered with paint will end up black.
Leave the completed painting to dry completely and then completely cover the entire piece of work with black ink. leave the ink to dry completely.
When dry hold the painting under running tepid to warm water, or use bottles of warm water. Keep moving the painting as the water runs on it. The ink will begin to run off all coloured areas. Some of the paint will run of as well so make sure your initial coat of paint is quite thick. You can allow as much or as little of the ink to run off as desired, depending on the effect you want to create.
I hope this information is useful, I'd like to see some finished pieces of work.