Jeff Bridges asks why tracker bars are brass and not aluminium.

I have a few piano supplies catalogs from the 1910s and 1920s.  Various
tracker bars are offered in each but for some strange reason the brass
ones are consistently cheaper than the silver ones.  Brass (an alloy of
copper and zinc) was used to replace wooden tracker bars used in early
instruments.  Mass producing wooden bars especially for narrower spaced
scales became impractical.

Brass was already used widely by musical instrument makers so the
technology to knock up a precision brass tracker bar was already easily
at hand by 1900.  I would speculate that brass is cheaper, more easily
workable and more robust than the other alternatives.  That said, plenty
quality player instruments (i.e., Aeolian) used brass.

Why not use aluminium?  Well, why bother when you've already got
workable and economical brass technology.  Look up "brass" on Wikipedia
for a brief oversight into all the different brass kinds and alloys and
their uses : it's quite a fascinating little entry to read over.

Welte and Hupfeld used what the catalogs refer to as "German silver"
(otherwise known as "nickel silver"), which is a bright-finish alloy of
copper, nickel and zinc.

The Ord-Hume book refers to the unlikely "Britannia metal" but that
book can be a little broad at times.  There are a terrific amount of
metal alloys in use today and also in the past, each with it's own
specific use.

Regards
Adam Ramet
www.themodist.com