Note: When I talk about washes/glazes, I an interchanging the terms. A wash is generally used to shade, and a glaze is used to tint. I use them both for similar purposes. (I'll wash and glaze at the same time)
After painting the metallics, just use badab black on them, and badab black (nuln oil) on the pants. And you are done.!
Optional: As with any technique, you can then go back and dry brush the washed metallics to give them a bit of pop, and add details such as eyes, tongues, etc. All up to the individual artist, and the quality you want out of your paint job.
I'm pretty exhausted!