I'm glad someone has responded because I wondered if I had purchased forgeries. I swear they will not blend on anything other than watercolour paper, I even used Ranger manilla cardstock. They go down on the paper surface like a childs felt tip pen and no amount of water will budge them, not even slightly. I've been using water brushes for years and at one point was so frustrated that I just squeezed the water brush to allow a big blob of water onto the ink, but nothing happened!
When I used them on stamps I got a nice mottled watercolour effect, but that was it.