Office of Steam Forum for Model & Toy Steam Gas & Hot Air Engines

Among the problems you may be experiencing is the actual composition of the brass itself, the method of creation, and the "temper" and surface
"case" that it may have, along with various levels of surface oxidation. The odds of your test pieces being the same as any old boiler you may be thinking of doing are rather remote. Still worth trying this wonderful experiment to its fullest, and as you say, if it doesn't produce the effect you are after, just polish it off and try again. Most boilers have large surface areas that are hidden in the firebox, so provide test areas that will be specific to that boiler, that will not show on the finished product ... good place to try looking for that just right color.

Honestly, I am having fun figuring it out. If I can get my solution close, it seems like variances in color come with time in solution. My first tries at anything other than store-bought stuff, and the colors you can produce are pretty cool.