It's difficult to see the photo close-up, but I would do it like sponge-painting a wall. I would use a small sponge and use several shades...gold (vodka & luster dust) and the different greens, etc. and just keep layering it until I got that look. I don't think airbrush is going to give you the "mottled" look needed.
I was also thinking sponge-paint.
you guys are awesome!! I NEVER would have thought about the sponge-paint, but you are totally right. I can't wait to do this ake.