Bronze is a blend of copper and tin and has different grades depending on how much of each metal is used !! More tin can lighten the bronze enough to give it that gold look similar to brass !! Most of the trains would have used bronze,, riding on a train was an event back then and more for the upper social class !! Top quality was the norm !! Your bootjack looks like typical bronze with the correct patina !! I would advise against cleaning it more !!