aluminium pans

Friend has blackened a bare aluminium pan by using oxiclean on it. Now my chemistry days are long past me. IIRC aluminium can be changed in colour by various things, but for the life of me, I can't remember what turns it back to that dull grey that looks like ally.
Can anyone help please.
Dave
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wrote:

Angle grinder?
Or, new for 2010: Pressure washer. ;-)
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I would try some steel wool on it and if it restores it then get a polishing kit for aluminium. If its a chemical change you might have problems though.
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Bruce wrote:

Another bloody keyboard to clean up, I didn't expect that :-)
Dave
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wrote:

Don't expect any sympathy from me. My all-singing, all-dancing Logitech keyboard still hasn't recovered from a serious dousing with cholesterol-reducing yoghurt.
(Tesco's own brand. Nothing but the best.)
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On Sun, 03 Jan 2010 18:00:25 +0000, Bruce wrote:

There's an answer to that: pressure washer!
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Dave wrote:

Wire wool and elbow grease.

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wrote:

Careful using steel wool on a softer metal such as Al? Same warning about using raw steel wool to scrub stainless steel. Small bits of steel get embedded in the surface and then rust! Maybe try a stainless steel scrubber (ss. steel wool).
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terry wrote:

If the cooking of something acidic doesn't work then I will recommend he uses Scotch brite made by the 3 M's company.
Thanks all.
Dave
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Dave wrote:

Cook some rhubarb or other acidic fruit in it, but don't eat it.
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"Cook some rhubarb or other acidic fruit in it, but don't eat it." Did that years ago with motorcycle engine cases and they came up lovely and shiney even the insides that had discoloured with years of being covered in hot oil.
Trevor Smith
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Terry Fields wrote:

That was in the back of my mind, but I couldn't remember what caused to to go black what to boil in it to take away the black.
Thanks
Dave
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On Sun, 03 Jan 2010 09:19:12 +0000, Terry Fields

Not eating rhubarb at all is the best thing to do with the stuff....
--
Frank Erskine

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On 03/01/2010 17:55, Frank Erskine wrote:

That's what I say to SWMBO but she still keeps growing the stuff. The black in the pan is I suppose Aluminium oxide so any acid should dissolve it e.g. lemons.
--
Tim

"That excessive bail ought not to be required, nor excessive fines
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On Sun, 03 Jan 2010 18:16:13 +0000, Tim Streater

Isn't aluminium oxide white?
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On 03/01/2010 18:28, Bruce wrote:

Apparently so. My mistake.
--
Tim

"That excessive bail ought not to be required, nor excessive fines
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Bruce wrote:

No. That's aluminium acetate or carbonate I think.
Normally al is actually protected by an ultra thin tough oxide layer that forms within minutes of it being cut.
That however is prone to acid and salt attack, and that's when you get Al corrosion.
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On Mon, 04 Jan 2010 11:05:50 +0000, The Natural Philosopher

I only asked a question because I thought it was more polite to the previous poster than making a bare statement. But a statement would have been appropriate, because aluminium oxide *is* white.
No question. ;-)
http://en.wikipedia.org/wiki/Aluminium_oxide
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Perhaps you could learn to read? Or did the terms "ruby" and "sapphire" mean nothing to you?
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Aluminium's "natural" oxide layer from air alone is weak, and takes an hour or two to form. It's easily disrupted afterwards by even gentle mechanical scraping.
Anodising is the deliberate assisted formation of the oxide layer. In particular, the layer formed can be made far harder than the naturally forming layer. Even a cheap bare aluminium pan will have had some degree of deliberate anodisation or passivation done to it.
Passivation is a similar process to anodisation (usually chemical rather than electrolytic) which also give a thicker, stronger oxidised layer than air or water exposure. Particularly for stainless steel, robust kitchen use of either aluminium or stainless depends on passivation - if you don't passivate, either metal will be prone to staining. Many simple kitchen materials are active enough to cause some passivation "naturally" on their first use, without you even noticing, but this isn't the same as simple air exposure. In particular, stainless ought to be passivated with uncoloured citric acid before something more colourful gets to it and makes a permanent stain.
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