I bought this pot a few weeks ago. I've only used it a couple times since, but yesterday I decided to boil some eggs in it.

I ended up forgetting about them for a minute, when I came back the water was not enough to cover them anymore. About 10% of the eggs surface were exposed to air, however, the pot was this very dark color.

I've never seen a pot blacken like that, at most something like a kettle if you let it run dry for a while.

The pot has what looks like a machined bottom, with some casting bubbles that you can see as the light spots at the bottom. Which leads me to believe this might have been caused by scrubbing, given the strange uneveness? But the coloring only manifested once I used it again.

By weight, and the fact it is so poorly cast, I think it might be aluminium, but there are no markings specifying the material of the pot. I even went back to the store and the label doesn't specify either.

The pot in question, with its bottom blackened roughly to the waterline

Close up of the blackened surface

  • Is the pot magnetic? If it is not magnetic, it is aluminum. If it is weakly magnetic, it is stainless steel. If it is magnetic, it is steel. You can also tell by weight if you have some experience with both metals. Aluminum is a LOT lighter.
    – DKNguyen
    Commented Jul 24, 2021 at 0:28

2 Answers 2


I am pretty sure it is the sulphur in the eggs that is doing this. It is present even in the egg shell.

When iron and sulphur react under heat, it forms iron II sulphide which is black (or brown) in colour.

  • 1
    @DKNguen, that may be true but if you are going to answer with that you need to provide a basis. Perhaps this would be better as a comment than an answer, unless you want to edit and add detail?
    – GdD
    Commented Jul 23, 2021 at 15:50
  • @GdD Is that detail enough?
    – DKNguyen
    Commented Jul 23, 2021 at 20:55

Uncoated aluminum pans are very prone to oxidization. Aluminum Oxide can be dark grey, or get close to black. Certain things can make aluminum oxidize faster, such as putting them through the dishwasher.

This is pretty common in uncoated aluminum pans. You can scrub it off, or soak it in water & vinegar then hand washing and drying. However, as soon as it's clean it will likely come back fairly quickly--though what you cook in the pot and how you wash and handle it could slow (but not entirely prevent) it from coming back.

Aluminum oxide is essentially "aluminum rust"... Though there are some differences. When iron gets that red iron oxide rust that we all know, it spreads and continues to degrade the iron. Aluminum oxide actually creates a bit of a protective coating and slows the further corrosion of the aluminum.

  • Interesting. Is it safe to use it in this oxidized state? The boiled water seemed to be clear, but chemically you can never be sure just by looking.
    – Kroltan
    Commented Jul 24, 2021 at 0:06
  • 1
    @Kroltan Aluminum oxide is the abrasive used in sandpaper sand and sharpening stones and is also what makes up rubies and sapphires. So though you might find eating out of a bowl made of abrasive unappealing (which is not as pure as it could be for most abrasive applications. Pure aluminum oxide of that form is white) it is basically the same as a ruby or sapphire bowl which you probably have much less issue with, sapphire being used as an exotic glass in some applications. Very unreactive. I'd be more concerned about consumption of actual aluminum.
    – DKNguyen
    Commented Jul 24, 2021 at 0:48
  • 1
    To avoid this problem, you want anodized aluminium, which provides a better protective layer and is common. Commented Jul 24, 2021 at 21:49

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