Same on my end, I did the metal bits last. The bone bits were the toughest for me to do because nailing the color was a chore. It's not a completely flat brown (its got shades of green, too) and to get highlights on the raised areas without taking so much of the areas around it off required some experimenting on my end.
For the most part, jaw and cheeks were done with several layers of various shades of brown dry-brushed on top of each other (all on top of a black base coat and an "antique white" color to simulate bone) and then lightly buffed with a towel. Then, on top of that, went on several washes to get into the recessed areas. Those areas were then masked off to do the metal bits and that was fairly straight forward: mask off, spray with chrome colored paints, darken with inks, and dirty with washes. Seal the whole thing off with some crystal clear.