I let the calcium-encrusted chrome plated hardware from my 1940-vintage tub soak in a solution called "Calcium Lime & Rust Stain Remover". Most of the calcium came off in a matter of 30 minutes or so, and there was no other damage, so I decided to let it soak for a few hours to get really clean.
Unfortunately, when I came back, the chrome was discolored to a light copper tint.
The active ingredients in this solution are hydrochloric acid and sulfamic acid. Does anyone know how to get the chrome back to its original color?