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I use a big aluminium pot to boil water. I think the water contains iron because after 4-6 months, the inside of the pot is full of brown stains. The colour is just like ferric. There are lots of circular brown areas (1-4mm diameter) in the pot.

  1. Is this stain caused by the iron in the water? If not, what is the cause?
  2. How can I remove these stains?
  3. Can I do anything to prevent these stains in the future?

Pictures

At the side Stain in real color Stain close up at the bottom of the pot

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Do you have a picture to share? That could help out a lot. –  Preston Fitzgerald Mar 13 '13 at 13:16
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@PrestonFitzgerald Pictures added. The pot is currently full of water so could not take more close up picture. –  shiplu.mokadd.im Mar 13 '13 at 20:51
    
@shiplu.mokadd.im It looks pitted in these photos... is it rough to the touch? or is it just a trick of the light? –  sarge_smith Mar 14 '13 at 3:53
    
@sarge_smith Its not pitted. Its a layer. Peeling the layer reveals shiny aluminum. But its very hard to peel. Yes its rough to touch. –  shiplu.mokadd.im Mar 14 '13 at 9:55

2 Answers 2

If it's rust stains or other kinds of scale build up, CLR will take care of it:

http://www.jelmar.com/CLRbasic.htm

From the pictures (thanks for adding) it looks like sediment from the water (source, pipes, etc) and CLR cleans it easily. Just don't breath the fumes.

Also, you can try commercial coffee pot cleaners such as http://www.urnex.com/ to remove the build up.

Finally, if none of the above is available in your area, try Vinegar first. If that didn't work, wash off and switch to baking soda. you may have to make a paste and let it treat for a while.

There is also this recipe for cleaning rust stains from aluminum pots, though I haven't tried it.

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How exactly would an ALUMINIUM pot rust? Even if it was building up aluminium oxide, he wouldn't want to clear it off since it will just reform. Not to mention that aluminium oxide couldn't form under water in the usage conditions he described. –  sarge_smith Mar 13 '13 at 17:28
    
@sarge_smith ALUMINIUM corrodes but not like Iron. The rust I'm referring to is external to the pot. As in Iron existing in the water, the pipes, or even an overused spatula. In some places the rust can build up in a matter of days. You might have also seen an under-used bathroom where the ceramic looked like it was rusting. Did you ask yourself there how could CERAMIC rust? –  MandoMando Mar 13 '13 at 18:00
    
That rust isn't rust, it's scale. It's what's formed by the evaporation of water and the mineral deposits that the process leaves behind. While this gentleman's issue might be scale (I doubt it actually, but anything is possible), it definitely isn't rust. Once again, unlike with many other metals, when aluminium corrodes into aluminium oxide, it forms a dull barrier that protects the aluminium. That's because it remains bonded to the surface until you remove it. It's almost as good a protecter as anodizing. Of course, almost all aluminium cookware sold is anodized so (cont) –  sarge_smith Mar 13 '13 at 18:20
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From Wikipedia: ...a thin surface layer of aluminium oxide that forms when the metal is exposed to air so the oxide is almost always present and the above answer is NOT about aluminium rust. It's about Iron Oxide staining an Aluminium pot. –  MandoMando Mar 13 '13 at 19:28
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I have added some pictures –  shiplu.mokadd.im Mar 13 '13 at 21:04

It's hard to say what is causing these stains without more information about exactly how you are using the pot. If you are just using it to boil water and nothing else, then the stains could be a result of the minerals in the water in your area. Also, if you are just using the pot for water, do you wash the pot in between uses? Repeated exposure to moisture can cause an oxidation layer to form on the surface of the metal. Cleaning the pan thoroughly between each use should help prevent oxide buildup.

The stains could also be caused by what you are using to clean the pot. Aluminum is a fairly reactive metal; so any acidic compound or residue that gets left on the material for too long is likely to cause a stain. You can read more about how to take care of your aluminum cookware here:

http://www.jesrestaurantequipment.com/jesrestaurantequipmentblog/cleaning-aluminum-cookware/

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