Copper won't rust.

You can use steelwool to scrape off the rust. You can spray with rustoleum, but I do not know if that will harm the birds.

Also, according to Rust-Oleum's FAQs, their "products are not suitable for continuous water immersion."

From what I've gathered on some other forums here on GW, you might be able to use the Rust-Oleum Primer for Rusty Metal as a base coat, as long as you eventually paint over it. Below is a link to one of the threads I found here which gives at least one personal experience with the stuff.

Hope you find some help soon! :) You might try a full site search here, in case there's more helpful info out there.

Brenda

Here is a link that might be useful: Cast iron birdbath - Garden Junk Forum

My wheel barrow rusted through 20 years ago and I laid up a glass fibre and resin coating and it is still going strong. al

If you REALLY want to get rid of 100% of rust on something, use electrolysis. It is somewhat complicated, but can be done with a plastic tub, a few misc scraps of wood and iron, and a car battery charger. Some people have these things lying around in their garage :) Here is some info: http://antique-engines.com/electrol.asp. Otherwise, scrub away, using a steel brush or steel wool depending on severity of rust. Use a rust remover like CLR or Naval Jelly to speed things along - but be prepared for a VERY messy job.

To coat your iron bird bath so it NEVER rusts, you are best off using pool paint or epoxy paint (two-part). These paints are specifically designed to be in constant contact with water (unlike Rustoleum). Pool paint can be found in any Home Depot, though it is typically either white or blue. I use this on concrete fountains and it dries to a fingernail polish hard finish that lasts for decades. If you want to go really hardcore, get some 2-part epoxy paint (food grade NOT marine). This is the stuff you can use in aquatic environments like koi ponds, large aquariums, etc. You can typically buy this from koi stores, or order it from many places online (it is not cheap but when you paint a pond you don't want to have to repaint for YEARS). DON'T get the marine grade because, though it is the same basic product, it will often contain algicides (to keep marine growth off the bottom of boats) and it will poison water left in contact with it (as well as kill fish if you use it in a pond).