You must have seen them, those gleaming metal-colored aircraft, polished chrome bumbers on an old Chevy.
Looking bright and shiny is exactly what you want to avoid when you need good camouflage - in any army. But this technique may come in handy, even for some military models or dioramas. To brush up your soldiers' cutlery, bajonets or mirrors...
Thin metal sheet is available in hoppy and artist shops in all colors and sizes... I never tried that, but I can imagine the results may be spectacular if you can apply this technique to ammo.... (tank shells).

I'd love to explain how it's done properly, but it would never be as impressive as what you'd find on this link :
http://www.up-link.net/~modeleral/Foil.html
Good luck !
Jan