Bare aluminum oxidizes the instant it is exposed to air. This layer of oxide prevents plating from adhering to aluminum. But you can zincate the aluminum, which removed the oxide and leaves a layer of zinc. the zincated part will be a dull dark ugly gray, but the aluminum beneath is now protected from the air. Next you do a nickel strike - the nickel solution etches the zinc away. Now you can plate over the nickel strike with chrome.
The chrome finish on plastic is actually aluminum, applied by "vacuum metallizing" in which the aluminum is evaporated in a vacuum chamber, forming a cloud which condenses back onto the plastic (or glass, ceramic, fibreglass, etc.) and forms a uniform layer which shines like chrome. A clear topcoat then protects the aluminum layer from oxidation. This is how automotive plastic "chrome" is made, along with toys, chrome plastic bike accessories, and flashlight/headlight/taillight reflectors.
Aldo Ross Middletown, Ohio
----- Original Message Follows -----
From: Chuck Schmidt <chuckschmidt@earthlink.net>
To: Classic Rendezvous <classicrendezvous@bikelist.org>
Subject: Re: [CR]Cinelli stem--alloy vs. chrome
Date: Wed, 04 Jan 2006 23:35:39 -0800
> I wouldn't expect it was very exotic. A long time ago
> (40+ years ago) plastic model car kits came with chrome
> (actual chrome) over plastic parts done with a vacuum
> process. And my friends and I used to get our aluminum
> valve covers on our cars plated with chrome back then too.
> Fairly common in SoCal.
>
> Chuck Schmidt
> South Pasadena, Southern California
>
>
> Kurt Sperry wrote:
> >
> > I'd forgot. And I wondered then and still do how they'd
> > done that when seemingly no one else had.
> >
> > Kurt Sperry
> > Bellingham WA
> >
> > <chuckschmidt@earthlink.net> wrote:
> > Here's a mostly chrome plated ICS Campagnolo group and
> > Cinelli stem:
> http://bulgier.net/