Hard water stains on copper with dark patina
We have these beautiful old hammered copper sinks that have an even chocolate brown patina. We also have terribly hard water and it has left this ring around the drain in the bathroom. I generally clean the sinks with either liquid hand soap or Mrs Meyers all purpose spray and it works well except for the ring. I am afraid to use anything more mechanically or chemically abrasive and ruin the patina. Does anyone have any ideas, or is the answer just to scrub the entire sink until it’s shiny and let the patina re-accumulate over time?