I have made several sets of bells and discussed the matter with Don
Stinson, who has made a great many.  He tells me that ordinary cold
rolled steel is as good as anything.

I cut them a hair oversize and then have the ends milled to give
a nice appearance.  Then I tune them a few cents sharp to give a more
brilliant sound, and finally have them nickel plated.  The plating
doesn't seem to affect the pitch much.

Wurlitzer and some other makers strike the bells near the ends, which
gives a clangy dissonance, while others strike the bells in the center
to get a more musical sound.  I prefer the center.

Fritz Gellerman