Regarding the post from Diane H Kay: Regina used steel to make their
discs.  They were either tin coated or copper plated.  The copper
plated discs are better disks but were more expensive to manufacture
due to a polishing operation after plating.  Tin coated discs present
themselves as dull to shiny silver in color, identical to an old tin
coated food can.  Both types of disc are generally durable and will
remain rust free in a dry environment.

You may have some discs from before 1900 that are made of zinc.
That material was abandoned about 1895 because the projections tended
to break easily.  The heavy dull discs you describe might be zinc.

You will need to describe the disk that does not play.  There are
several types of discs other than the Regina style.  Almost all have
some sort of projections below the disc to pull the starwheels.  But
there is also a design that has no projections which is probably what
you have.  Do not try playing discs made for another style of music
box.  The Regina 11" and 15-1/2" music boxes will play Regina discs and
Polyphon discs.  The size is the measure of the disc diameter.

Also, as you are new to the music box collecting hobby, I will advise
you to not oil the music box, especially do not oil the starwheels.
The oil will collect dust, which is abrasive, and cause damage.  Music
boxes do need to be maintained, but this should be done after some
study or by a repair specialist.  A cleanup and oiling once every
twenty years or so is what's needed.

I recommend you join the Music Box Society International and a local
chapter of the MBSI in your area.  You can join a local chapter after
national membership is taken care of.  You will learn many things about
your music boxes and other music boxes as well.  You can find
information about the Music Box Society at http://www.mbsi.org/

Enjoy your collection.

Don Shenbarger