I wanted to experiment a bit with weathering techniques on this – but to keep it fairly understated. I think, when it comes to special effects, less is more:
As you can see, I used masking fluid, duabed-on fairly arbitrarily with a cocktail stick, to create the random chips and divots; then various washes and pigments to add colour – mainly purples, browns, and oranges. I also flickered-on blotches, using an old paintbrush:
Once the washes had dried, I stippled metallic paint on in some places, and used a small piece of sponge in others. Nothing too fancy – but it still looks pretty effective, all told.