This article is from the Miniatures Painting FAQ, by Brenda Klein email@example.com with numerous contributions by others.
For fantasy and historical, some suggest not priming the miniature,
then washing or drybrushing (or both) the bare metal, but to others
this looks sloppy and unfinished. Besides, not much armour looks
like lead, and lead certainly doesn't make good armour (nor do any
of the alloys of which miniatures are cast).
Paint the armour a base-metal colour, usually silver or one of the
like tones, and let it dry. Don't be afraid to use bronze, or gild
it, though. Then take a black wash (ink is excellent for this) and
go over it carefully. Let that dry, then take either your original
colour or a lighter shade and drybrush. Remember to use a seperate
water/thinner for the brush you're working the metallics with, so
as to not get flecks in the other colours.
Steve Gill (firstname.lastname@example.org) shares his method of painting
a) If the links are sculpted clearly enough that you can see the
leather underneath then base coat should be leather (whatever colour
required by the figure). If not ignore this step only paint leather
around the edges where it should show under the links.
b) The links are painted in dark metal.
c) Drybrush the links in lighter metal.
d) Highlight drybrush in very light metal.
In general I would choose gunmetal as the dark metal, steel as the
lighter colour. Heroic figures could use steel with silver, but try
to keep this rare.
Darker chainmail is probably much more historically correct than the
usual hollywood style silver armour.
Dan Evans (email@example.com) has a method suitable for SF figures
as well as fantasy: "I've come up with a way to get interesting
results with metallic colors. (Maybe someone else has done this
before...) Basically, the trick is just two steps:
1) paint your figure (or part of it) silver.
2) when it's dry, apply colored ink (I have the Citadel set) over
the silver. The cool part is, you get unusual control over the
degree of tint by applying the ink straight from the bottle or by
watering it down (a wash.) Another cool part is, you can blend one
color into another. Suppose you have a warrior with a shield, and
you want it to fade from metallic blue at the top to metallic green
at the bottom. Paint the whole shield silver first, and then when
it's dry, apply blue ink to the top half. Next, apply green ink
to the bottom half, mixing it up with the blue in the middle.
"Yet another cool part is light-to-dark shading done this way:
Suppose you have a Space Marine and three shades of silver paint.
(The shades of silver may be sold as "aged metal" or "chain mail" or
"gunmetal" or "silver". Use your eyes: buy a blackish silver, a dark
silver, and plain old silver.) I'll just call them dark, medium,
and light. 1) Paint the entire figure with the dark silver and let
it dry. 2) Drybrush the entire figure with the medium silver and
let it dry. 3) Drybrush the entire figure again, concentrating on
raised details, with the light silver and let it dry. 4) Right now
your Space Marine should have a pretty nice shaded metal look. Now
go over the whole figure with red ink, and you'll have a shaded RED
metal Space Marine. Hey, you could even try technique B at this
point, maybe with purple or orange blended into the red."
There is a caveat to this, however. Be careful using inks with acrylic
metallics. There is often a reaction between the two which give some
nasty effects. At the very least allow the metallic to dry for 24 hours
before adding inks. Some people have had only bad results from inking
over acrylic metallics... Test it before you begin your masterpiece.