Gray Powdery Residue on Cookware...why?

dynamicduoSeptember 27, 2007

We have had a Miele dishwasher for about a year and a half now, using Cascade liquid gel for detergent. During this time, we have noticed almost all of our pots, pans, pie plates, and even our metal garlic press have developed a whiteish gray finish on the outside, and some of them when wiped will actually release a grey/black residue.

I am sure this isn't healthy, and we will need to throw out these items. But does anyone know why they are reacting this way? I have read very little about aluminum based products reacting this that whats going on here? I guess I am just even more curious as to why its now just happening with the Miele dishwasher.

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Pie plates? Metal garlic press? Those items, and the others, wouldn't happen to be aluminum, would they?

    Bookmark   September 27, 2007 at 12:49PM
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I would imagine so, or at least have aluminum in them to an extent.

    Bookmark   September 27, 2007 at 1:10PM
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Yep, that's pretty much what aluminum does.

That would be why people buy expensive cookware with stainless steel cladding covering up the aluminium. (Or, even better, covering up copper, but that's a whole 'nother thread.)

    Bookmark   September 28, 2007 at 12:46PM
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Aluminum and knives are the only things I don't put in my dishwasher. I suggest you do the same. The dishwashing detergents will corrode and pit the aluminum.

    Bookmark   September 29, 2007 at 2:18PM
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Yep; as stated above, that residue is a product of a chemical reaction between the dish-washing detergent and aluminum cookware.

In the chemical reaction between soap and aluminum ATOMIC hydrogen is formed. Atomic hydrogen has a very weird property of actually being able to move completely through solid aluminum......because it is such a small particle. Atomic hydrogen cannot be contained in an aluminum moves right through it as though it weren't there. It remains in the atomic state only until it meets another atomic hydrogen atom which then produces the hydrogen molecule H2. Molecular H2, which is a gas, cannot pass through solid aluminum. This process of hydrogen going from the atomic form to the molecular form causes the metal to actually flake (sometimes even crack) helping produce the powdery residue that you saw. The hot water in the dishwasher greatly accelerated this reaction.

Soak is OK to use on properly seasoned cast iron, but must be used with CAUTION on cast, or coated aluminum cookware. Soaking SCRATCHED Teflon coated aluminum cookware in soapy water will cause the Teflon to rapidly separate from the aluminum........but this another whole new thread onto itself too.

What I have just revealed is based on solid chemistry and science. I have dealt with this type corrosion mechanism on major industrial processing units in my former career.

Bottom line......don't wash aluminum cookware in a dishwasher. Don't soak your scratched coated aluminum cookware for too long either......leaving it soaking in soapy water will accelerate the deterioration of the coating. Don't soak cast aluminum either as it will cause pitting.


    Bookmark   October 1, 2007 at 5:29AM
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Thanks so much, really! I appreciate the insight and will consider it a lesson learned.

    Bookmark   October 7, 2007 at 10:48PM
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