Aluminum pot discoloration

Several of the chemicals used in dishwasher detergent react with aluminum. I have several aluminum backpacking pots that turned a mottled grey-blue after a turn the dishwasher. If the aluminum is anodized the reactions are slowed but still will occur over time. I routinely put Calphalon cookware in the dishwasher and over time the coating has eroded to the same patina as on my backpacking pots. All of the cookware still works fine even though it is a bit ugly. If I recall, the coloring comes from a combination of largely insoluble aluminum oxides, aluminum hydroxides and aluminum phosphates. A chemist would know more about this than do I, however.

Don't wash your aluminum cookware in the dishwasher. Dish-washing detergent is very abrasive – it actually has an abrasive compound, this will REMOVE the anodizing from your aluminum cookware in many cases! Most manufacturers recommend hand washing.

Yup. I've ruined a good hard anodized kitchen skillet with dishwasher detergent. The stuff is heavily alkaline. A green scrubby sponge usually does the trick on the tough stuff.

As to abrasives taking anodizing off, I got a pot that had stuff baked to carbon on it and I tried cleaning it, just to see what it would take. I did remove the anodizing after some very heavy work with a Dremel tool, which was light years past anything you could do by hand. Good hard anodizing is amazingly tough: you can damage it, but it takes some abusive effort to go there.

"Cascade is now phosphate-free, as required by new legislations across the whole industry. One benefit of Phosphates in dishwashing is its ability to help protect the surface of metals. With the removal of phosphates, discoloration on aluminum may now occur faster than before. Some good news is that discoloration does not affect the food being cooked." –Cascade Consumer Care, August 12, 2010

How to clean:
http://www.ehow.com/how_12189119_clean-aluminum-after-dishwasher-turned-dark.html

Me? I like my aluminum cookware dark. "Poor man's anodizing."

Dishwasher definitely has an affect on AL pots. If you would like to give it a uniform dark color all the way around, make a large pot of tea and soak the pot in it. Cover the whole thing up though! Or make some spaghetti sauce, let it simmer for a couple of hours, and throw your pot in it. The acidity of the spag sauce will help too…

Wish I still had the pot I used to make tea in, used it for years. I drink a lot of iced tea and used to make it exclusively in an AL pot. The interior of the pot was a dark charcoal grey due to the tea. Also used that same pot for spaghetti sauce from time to time. The darkness of the AL I found kind of charming.

I was at REI during their garage sale, found a 1.4L Aluminum pot which was new, got sidetracked, put the pot down inside the store, no more pot. New, not on sale, was $15 and weighed nothing. Old aluminum is not supposed to be shiny, it is the charming nature of being used that makes it attractive! :-) Age it baby, hang on to it, and pull it out of your pack 20 years from now and say that is my pot… the miles it has seen!

Oilcamp and Open Country still turn out cheap and light Al pots. I found this 1.5 liter no-name example that is 3.8oz plus 1oz for the lid.

So, searching the inet, I can't find anything more substantive than complaints (mostly by hysterical housekeepers swapping rumors) about darkened aluminum. If it is oxidization as I suspect, then there should be some (perhaps small) protective effect to the darkened aluminum, just as a nice patina on a carbon knife blade helps ward off rust to a degree. But I have been unable to confirm this possibly positive side effect.

An inexpensive stainless steel wire brush is an easy way to clean off the darkened surface of aluminum. As noted above, there does not seem to be any real health or safety issue with the darkened aluminum. But if you want to make your pots shiny again the wire brush is very effective.

Here is an aluminum beer can that was deliberately darkened on the bottom with tea water (the idea was to see if dark aluminum would absorb heat better):

Here is the same can after a couple of minutes with the wire brush:

Over time, the transformation can become so "thick", materially integrated, no wire brush will take it off. I am putting a pack together shortly for GGG in So Cal. I will see if I can find my aluminum pot that I have used for YEARS. Got it from a guy that was ditching his camping stuff who used it for YEARS. It is still going strong… great pot for car camping, wish it were smaller and the handle came off. Post later. You are gonna laugh. Pot looks like absolute HELL, love using it though! Makes me laugh every time I pull it out.