Thanks to The Science Goddess and Allen for their help with the experiment problem I was having. One of the links Allen provided showed how the same effect can be created using a black marker and some water, while the Science Goddess' suggestions greatly cut down on the amount of time and safety gear required for this lesson.
The picture at left shows one of the early results. Although we didn't get the red I was hoping for we did get some nice orange and yellow, and it was more than we got the other way. Now if someone could show me a way to capture the results a little better. Snapping a picture of it didn't work out too well so I placed it on a flatbed scanner. This picture does not show the results as well as they really looked.
Thanks again for those who offered help.