Hi!
Maybe some of you already hear about oil washes,
imo it's one of the best tehniques to achieve nice metallics easy way.
How I use it:
1. I paint all "metal" areas with vellejo liquid metalics, this paints are awsome, one layer is enough to make a smooth cover.
The only one minus is that you'll have to use isopropyl alcohol to dilute it or wash brushes.
2.Next step is to get some oil paint, you can buy it in any artist store.
3. Than I simply dilute it to wash consistency with a few drops of gasoline (yup, gasoline!), you'll have to practice a little bit to get the perfect proportion.
4.Last step after covering whole metal area with wash is to carefully wipe it with soft tissue, try to keep only the deepest areas fully black.
You can experinet with different wash colours and consistency, brown colorus are perfect for gold metallics.
Hope you like it!