aluminum "tarnish"?


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Old 06-03-20, 04:12 PM
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aluminum "tarnish"?

Didn't know where to put thsi so I thought I'd throw out here.

When handling aluminum, such as bar stock or unpainted aluminum window frames, your hands get a dark, almost black film like coating on them. What is this called? It pretty much washes off. Might take two washings with soap.
 
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Old 06-03-20, 05:02 PM
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Its oxidation. Just like copper tarnishes and steel rusts. Cameo aluminum and stainless cleaner is a good cleanser to use on aluminum pots and pans. White vinegar is also said to work well.
 
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Old 06-03-20, 05:26 PM
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Yea, but a bit more!

Rust, which only occurs with metals with iron, slowly disolves the base material, aluminum corrodes creating a layer of oxide that acts as a protective barrier.

That is why iron needs a protective coating (paint/plating) to survive where as aluminum is more of a cosmetic treatment!
 
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Old 06-03-20, 06:24 PM
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What's odd about is the way it transfer to your hands almost immediately. Today I was handling a lot of it and when I looked at my hands they were black. Yet the aluminum looks as shiny as ever.
 
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Old 06-03-20, 06:43 PM
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You must have not climbed many aluminum ladders before.
 
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Old 06-04-20, 03:29 AM
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Yet the aluminum looks as shiny as ever.
Its all about the alloy, pure aluminum is reactive with water!
 
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Old 06-04-20, 05:38 AM
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The aluminum's oxide layer is quite soft which is why it easily rubs off onto anything. Anodizing performs a similar job but is much harder so you don't get the black dirty marks when working with anodized aluminum.
 
 

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