Use school glue gel, salt, & liquid watercolor on watercolor paper. The glue makes the colors rise from the paper and the salt creates a 'starburst' look. Rubbing alcohol on wet water color is cool too.
I could also see this used on making our cards. Wipe a stamp pad across the bubble wrap and press onto the cardstock. Bubble Wrap Paintings - paint with acrylic or tempera on sheet of bubble wrap. Press clean sheet of paper on top.