Hey, You Got Your Chrome in my Naval Jelly!

So I was cleaning some rust spots off my bike with Naval Jelly[sup]*[/sup] rust remover, which does the job nicely on the steel frame of my bicycle. Then, while reading the label, I notice that it says “Not for use on chrome.” Since some of my bike components are chrome or Cr-Mo alloy, I was curious but not really up to destructive testing (if that was what it might entail).

I was wondering if this advisory was meant more as a, “This is for oxidized iron, you dolt! It won’t work on anything else, especially not chrome!” or if it’s more like, “If you put this stuff on your chrome the resulting explosion will turn your hands green and make your tongue fall out. Don’t say we didn’t warn you.”

The main active ingredient appears to be Phosphoric Acid, and there’s also some Sulfuric Acid in there, too. (MSDS in PDF, JICYWTSI)

I don’t recall enough Chemistry to know what could happen if you try this – would it damage the chrome or just have no effect?
[sup]*[/sup]Naval Jelly is a registered tradmark of Henkel Consumer Adhesives, Inc. Not to be confused with Navel Jelly, a disgusting but oddly intriguing concept.

Well, I have heard that Naval Jelly will turn chrome black. I imagine that this is oxidation (sulfuric acid is a powerful oxidizer), but I can’t say for sure.

Steel, on the other hand, has a complex chemistry that may very well benefit from a little oxidizing.

Chromium is a rather valuable metal and is ususally used as sparingly as possible. Unless you have something like stainless steel, where the Cr content is >= 12-13% of the bulk, it is usually as a plating material. Cr is favored because it forms a stable oxide that does not expand and spaul off like Fe(x)O.
The caution is not that it won’t clean the Cr surface, rather that it will remove it.