What kind of stains are on what metal?
Would love to help, but need more info.
Do you mean Stainless Steel? This article may help: https://www.thespruce.com/remove-brown-stains-from-stainless-steel-1900549
If it is rust, soaking them in white vinegar for 24hours does the trick.
What metal is it & what kind of stain? really need to know more info. ( depending what it is it could rust it more soaking some metals in vinegar is how you get them to rust-age them https://www.jalopyjournal.com/forum/threads/caution-when-using-vinegar-on-rust.273354/ )
Hi Bridgid: Here's a site I found that might help, and it's from other hometalkers:) https://www.hometalk.com/2534786/how-to-clean-stainless-steel Good luck