Chris, this is a description of the construction I was given a while back:
Aluminium badges are cast in a mould and then anodised by an electro-plating process. Two-colour badges are first fully-plated in one of the colours by attaching an electrode and dipping them into a liquid solution for that colour (e.g. gold colour). The badges are then removed from the solution and the parts of the badge that are to stay that (gold) colour are painted (masked) with matt black paint. The badge is then electroplated with the second colour e.g. silver. The second (silver) colour sticks to and permanently covers the first (gold) electro-plate, but the second colour does not attach to the black paint. The black paint is then removed, allowing the original (gold) colour the show through.
I suspect 'staybrite' is a commercial name, AA being the actual process.
There are apparently a couple of articles in The British Button magazine / journal from the 1950s which gives technical details. I've been looking for them for a while, if anyone does find this mag / articles, I'd be grateful for a copy
Julian
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