[davec2]

Hello Chris,
When talking about solder, we have to be more specific, on brass and steel etc, you can use soft solder ( lead solder ), low melting point, this is similar to the type used in electrical joints, it leaves a grey colour and can be very corrosive.
There is silver solder, which is used in the jewellery trade ( and by myself ), this has a higher melting point, varying around 600 degrees and then there is braze, this has a higher melting point than silver and was widely used when badges were originally manufactured.
Of course, when badges were first produced, I'm sure they were all discoloured by the heat and would have been pickled to some extent, after being handed to the original servicemen, the badges would then begin to age, hence the ' patina ' that all collectors like today !!!!
I would have to guess at how the sliders and lugs are fitted to staybrite badges and I would assume the manufacturers use an epoxy designed especially for aluminium.
That's all I can tell you, I was a welder/fabricator for over 25 years so I do have a little experience with the different jointing mediums and have, in the past, welded just about every type of metal known to man.
If there is something I have missed, this thread will, I'm sure, highlight it.
Regards.
Dave.