Watersoluble Graphite Pencils

I bought a set of these pencils (Cretacolor) back in July and had not even given them a test run yet!! Yesterday my friend, Irene, and I went to DBs in Pasadena and I talked her into buying some and so figured I probably should try out my own set - LOL! Last night I drew this simple little still life using the 4B pencil. After the initial drawing, I wet it with a brush and water and let it dry completely. Then I used the 8B pencil to add some darks and brushed those areas with water. Once water is added, the graphite is "set." When water is added, the lines just instantly melt -- it's really neat! Now that I've given this new/old toy a test run, I'm eager to try something a bit more complex. Kate's watercolor pencil class starts in a couple of weeks, so I'm gearing up for that and now am wondering what would happen to do a mixed media with these pencils and watercolor pencils or tube watercolor -- the graphite could certainly be effective as an underwash for shadows!!

Here is where I bought my set http://www.fineartstore.com/Catalog/tabid/365/List/1/CategoryID/13320/Level/a/Default.aspx