What is the type of art used by swirling paint over water and dipping paper into it?

Years ago I saw something like this on a tv show where the artist dropped paint(acrylic or oil, I'm not sure) into a pan of water and swirled the paint into beautiful patterns then slowly placed paper over the top and brought it out again to dry. This resulted in a beautiful painted picture but I'm not sure what the technique is called. Is anyone familiar with this type of art and what is it called and how is it done properly as I'd love to experiment for myself.