I had some 4"x4" artist watercolor paper tiles, so I decided to use those.  I experimented with different media, but used purple in each piece for some continuity.  There is graphite on every piece.  For the two top left pieces, I used acrylic paint and gel pens.  The two top right pieces are made with tempura paint sticks and acrylic paint pains.  For the bottom left I used watercolor paint and alcohol markers and I used watrcolor pencils and waterbased markers for the final two.  I could have tried more, but it was getting pretty late!