I bought a giant copper kettle weighing about 35 pounds. It had an unattractive patina and crusted baking residue so I decided to clean it. This was no small task and in order to shorten the time I used hydrochloric acid instead of phosphoric acid. The final color is a rather ugly orangish brown rather than the reddish color I get when I use phosphoric acid. I've done muntiple rinsings and steel wool buffings yet the color remains. Any suggestions?