Buy a gun blueing kit from Canadian tire, and follow the directions. That's what I did with my Desert Eagle's Zeke's metal slide.
In the first pic you can see the Zeke's brownish finish. In the second, you can see where I didn't de-grease it properly, so I will have to do it again, but the second time around it's going to look bad ass. Either way it gives you an idea of what can be done with aluminum or steel using a gun blueing kit.
Before:
After:
__________________
Team Bad Karma(BK-09)
CAUTION: Evil Genius at Work
Those that wear the "Tin Foil Hat" stand on guard for thee. All others stand on guard for themselves.