Peter Fairbrother wrote:

Is there an easy way to remove zinc and/or cadmium plating without affecting
the steel underneath?

Very easy. Go to the supermarket where they sell cleaners and find a can of
Red Devil lye. That's about a pound give or take. Add it to about four gallons
of water and drop your parts in overnight. The zinc will be entirely gone and
if there was any rust on the steel that will be gone too. You can certainly
use acid but I don't like to use acid for this because the acid eats the steel
too and you have to really worry about neutralizing it. The lye doesn't eat the
steel so if you leave it in too long it doesn't hurt anything, plus the rust
gets chemically reduced back to iron, not eaten away.

It's nice if you neutralize the chemical before disposing of it. Don't dump
it into a storm sewer, make sure it finds its way to a sewer treatment plant.

I have done this myself, recently, worked perfectly. Be aware that whether you
use a base (lye) or an acid (e.g. muriatic) one splash can blind you, so wear
goggles, use good chemical proof gloves, and wear old clothes, and don't do
this anywhere near where animals or small children go.

GWE