Take it as another proof of my statement that metal gives very nice contrasts in black and white. It's a rooftop with a long slope reaching all the way down to the sidewalk (where I stood, of course). The rounded shape permitted less light to reach the bottom end of the slope and at the same time provided a distinct highlight almost exactly where the weldseam is located. But handle with care: The diagonal lines give a lot of dynamic and drama to the scene. It is almost like a collision the moment they hit the other diagonal line that forms the little triangle top right. I knew instantly that's a keeper before I even touched my camera.