Etching rhodium with Multi-Etch®
I originally perfected Multi-Etch® for titanium production. It’s a nonacid (pH 6.8) alternative to hydrofluoric acid. I’ve also tested it on other metals with great results.
I have not tested Multi-Etch® with rhodium plating, but I have used it to clean iron contamination from platinum without removing any platinum ions. I believe there would be a similar effect with rhodium.