[huntress]

Rust from cold steel will not hurt your birds but any metal in the system from chewers is not good. For hatching chicks it would be OK - they dont chew. The best way to clean it is to simply wire brush the heck out of it and wash it with a good bit of vinager wash. Remove any loose rust and leftover paint with the wire brush. Get into any corner. Then you can paint it with paint declared safe for childrens toys (spray paint). Hold a piece of cardbord behind it to help as you spray. Do this outside away from your fids and apply a few coats. Allow the cage to dry and cure for several days before putting any birds into it.
I rehab cages all the time. I still would not keep a heavy chewer in it for too long but its great for finches ect.
Word of advice - choose a color close to what it is or was and you will not need so many coats of paint but use a minimum of two coats. If you use a rusty metal primer allow it to cure for several days BEFORE adding the paint color coat.

People wine about rehabing old cages but to tell you the truth how many cages are out there new that we have not tested for lead from China???? Many. At least when I am stripping and repainting an old cage I know the paint I use is lead free?