The chrome plating process is done in three steps, after polishing.
1st, a copper plate. This can be done thin, or heavy and repeatedly to use
as a filler to sand out defects on old or pitted parts.
2nd, a nickle plate for the color. Nickle is soft and easy to scratch, but
this is was the final finish until sometime in the mid 30's.
3rd, chrome has been described as a "hard clear coat" over the nickle,
giving a brighter and more durable finish.
This is where the redundant phrase "triple plated" originates.
This process can be applied to nearly anything, leather baby shoes, wax
forms, etc, if care is taken to avoid high temps in the tank.
I find that aluminum tends to peel after a few years outside or on an
engine, so prefer to polish it.
--
Stupendous Man,
Defender of Freedom, Advocate of Liberty