To be honest, I liked Trapjaw's original colors (despite the fact that they didn't really make a whole lot of sense) so I wasn't quite sure about this customization in the beginning. Fortunately, I stuck with it, trying to enhance the Frankenstein vibe he gives off. I wanted Trapjaw to look like he'd been around for a while, hence all the rust.
Painted using a lot of washes. The rusted metal parts were sealed with dullcoat, the flesh parts with Krylon Matte which is a little glossier. The contrast makes the skin look a little nastier. Had to photograph him under low light so that the skin details wouldn't get bleached out.