More browns and yellows blended to make the brass. It looks very dull here, but that's the key to making things look shiny, make most of it dull so that the bright spots look bright by contrast. The background is painted blue, the square frame is straight out of my sign painting playbook. Create a margin and then exceed the margin. It creates the illusion that the octopus is even bigger than he really is and there's a layer of depth. The blue is far distance, the frame is middle distance and the Steampunk Octopus is close up.