I'm no expert, but I've been given to understand that the combination of friction by a very soft metal (like aluminium) with the acidity of the vinegar or cola works as a very mild abrasive: it removes anything on the surface but leaves the metal unscathed. Perhaps it's to do with the fact that the foil is softer than the chromed item, so it kinda 'melts' away with rubbing, removing grime in the process. So far, it seems to work - there doesn't seem to be any mark on my hoops, no matter how hard I look (even with a magnifying glass). Alex
Thanks, Alex! Since I have never tried this method, I bow to your expertise. I've never seen the Grand Canyon or the pyramids but, I know they exist. I appreciate your reply very much, sir. Not sure that I'll ever try it but, thanks again.
Brian