I'm vigilant about cleaning my stainless-steel All-Clad cookware, but sometimes I get rainbow-colored or cloudy white stains that I can't remove. What causes these stains and how do I remove them?
I called Bill Groll at All-Clad Metalcrafters in Canonsburg, Pa. Because he is vice president of technology, one of his corporate responsibilities is to stain the company's pots and pans and then figure out how to clean them.
Groll said your "rainbow" stains are actually very thin layers of caramelized oil. Like a glass prism, the oil refracts light at different angles, causing a rainbow effect. The cloudy stains, he guessed, are probably protein residue.
It so happens that I have a small stainless All-Clad saucepan that recently has been plagued by some faint stains that no amount of scrubbing with a nylon brush has been able to remove.
I poured an inch or so of distilled white vinegar into it and left it for about 10 minutes. Miracle of miracles! The stains vanished.
Before I discovered the miracle of vinegar, I had always attacked my stainless steel's stubborn stains with a cleaning powder called Bar Keepers Friend, which is, in fact, recommended by the makers of All-Clad.
Unlike vinegar, it is ever so mildly abrasive, but, unlike most other scouring powders (e.g. Ajax, Comet), it contains oxalic acid, which apparently performs that same acid magic on stainless steel.
Note: The preceding discussion pertains only to stainless-steel surfaces. All All-Clad cookware has stainless interiors, but the exteriors of the MC2, LTD and Cop-R-Chef lines are made from, respectively, brushed aluminum, anodized aluminum and copper. Bar Keepers Friend is recommended for the exteriors of all but the Cop-R-Chef; for that you'll need a brass-copper cleaner.
Erica Marcus writes for Newsday.