Painted on a 7 1/2" x 9 1/2" piece of All Media Artboard, a thin but sturdy board that's coated and works well with watercolors and other media. I worked on this some yesterday (it's been sitting not quite done for a while now and I forgot about it).
My chiropractor has photos of the big paddlewheel boats like the Delta Queen on his walls in his waiting room. I think he should have artwork featuring backs, don't you? Think I could get him to go for this and I could paint several women and men from the back and make them interesting and I could recoup some of the money I've been spending at his office every week?!? :)