Painting, concrete/striped: Now with guest artist.
Updated 2018-11-02: New photo.
Read on for explanation ...
Guest artist explained: Astrid made an A3 size painting and turned it over to me. I soaked it in water, curled it up into a ball, untangled it, cut it into stripes (and did the exact same thing with an A3 size painting of my own). Then, I assembled the stripes from each of the two paintings and glued them onto a single piece of A2 size paper.