Gold photos don't usually show true color so, it's hard to tell. To me, the gold on the piece on the right looks much, much heavier than the left one. The right one is more matte and has great color, both of which are often indications of thick gold. The left one has terrible color and it looks so thin that it's brightness is due to the bright nickel underneath the gold. On the older, thicker stuff, you often find gold directly over copper, without the bright nickel layer. These are generalities and there are exceptions.
I don't know what they use as a gold substitute on jewelry. If metallic, it would HAVE to be a copper alloy. Any copper alloy without a clear coat would have to tarnish or turn green except maybe aluminum bronze, which is yellow, looks nothing like gold, and wont plate. If non-metallic, it would probably be super shiny and really be off color.
Nothing yellow I can think of will damage the stripper and almost nothing on earth could be damaging to AR. The sulfuric is so strong that it becomes saturated with only minute amounts of base metals dissolved in it.
