Hi,  There was a post asking the merits of zinc discs vs. steel discs.
There should be no noticeable difference in sound quality between
a zinc disc and a steel disc as the information recorded is in the
projections, of the disc, the sound quality comes from your machine.

That said, there are reasons for wanting either type of disc.
Steel discs tend to receive rust and many of them are rusted beyond
recognition: you can no longer read the disc titles nor the emblem.
Zinc discs (and copper, for that matter) do not rust; however, the
projections are weaker as the zinc itself is weaker than the steel.

One of my best discs is missing about 5% of the projections and it's
very noticeable.  (It's the "Wedding March" from "A Midsummer Night's
Dream".)  I will probably get around to fixing it soon, as a friend of
mine is getting married and would like to have this disc playing after
they finish under the chuppah (wedding canopy).

Eliyahu Shahar