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Jan 12, 2010 09:33 AM

Gray residue on aluminum sheet pans, pots, saute pans and garlic press

I hand wash all of my aluminum pots, pans, and utensils, using Dawn dish detergent. I've never put any of them in the dishwasher. Within the last 6-7 months, I've noticed a gray residue on the sponge and cloudy dishwater when I wash them, and on the towel when I'm drying them. I'm wondering if this is normal or if it's harmful and I should toss them and get new ones. Anyone have any experience with this?

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  1. that residue is a product of a chemical reaction between the dish-washing detergent and the aluminum.

    it's a chemical reaction between soap and aluminum, involving the formation of atomic hydrogen particles. no need to get into the heavy, detailed science, here, but basically it eventually causes the aluminum to flake, which produces that grey residue.this is why the better aluminum-core pans are clad in stainless steel - to protect the aluminum.

    the bottom line is that detergent + hot water will eventually degrade/dull aluminum, and produce that residue even if you don't put the items in the dishwasher.

    25 Replies
      1. re: Davwud

        oh right, i should have addressed the safety factor! thanks :)

        consuming aluminum powder (or most industrial metals, for that matter) isn't exactly good for you. once you see that kind of flaking, it's probably best to replace the items.

        1. re: goodhealthgourmet

          That's what I was afraid of - the trashcan will be a little heavier this week. Thanks for the info goodhealthgourmet!

          1. re: bucksguy14

            yeah, i hate to tell people to trash things, particularly in this economy...but in this case i think it's the safest thing to do. and make sure your replacements are the best quality you can afford so that they'll last longer!

            1. re: goodhealthgourmet

              I've already ordered stainless steel replacements. I'm not going to replacement aluminum again. Thanks, again, for the info.

            2. re: bucksguy14

              Ummm, if they're aluminum they're recyclable. I wouldn't go that far though, scrub them good with a scotchbrite or similar to remove the surface oxidation and they should be fine.

              1. re: Scrapironchef

                Scotchbrite and Dawn are the only things I've ever used on them! Didn't think about the recycling aspect - they'll be in the bin Tuesday morning - thanks for that tip.

                1. re: bucksguy14

                  I'd try a different dishwashing detergent first, I use Joy and have never had a problem. I use my half sheet pans constantly as well as a couple of roasters.

                  1. re: bucksguy14

                    I'd verify that your recycling program accepts aluminum in forms other than cans. A lot of them don't, or have other places to recycle shapes they consider "scrap metal" instead.

                2. re: bucksguy14

                  Do NOT throw it out. The grey residue is perfectly normal when washing uncoated aluminum and it isn't harmful.

                  You can send them to me.

                  1. re: Kelli2006

                    I was tempted to say the same but it seemed the OP's mind had already been made up.

                    1. re: Scrapironchef

                      I hope that the people are are agreeing with the OP don't plan to eat out because uncoated aluminum cookware is ubiquitous in commercial kitchens.

                      All-Clad, and such might be common on Food TV but 99.5% of commercial kitchens use generic Wearever/Lincoln pots and pans, and the line cooks don't bat an eye before cooking acidic tomato products in uncoated aluminum.

                3. re: goodhealthgourmet

                  it's happening to my tortilla press but I line it with a plastic bag.


                  1. re: Davwud

                    that's a great way to get around the problem! it's too bad you can't do the same thing on the stovetop ;) but at least bakeware can be lined with parchment or foil.

                    1. re: goodhealthgourmet

                      It's also not too bad. It's just got a matted finish now and no longer has a smooth feel to it. You don't get anything on your hands if you touch it.

                      It's also less than 2 years old so I'd hate to toss it so soon.


              2. re: goodhealthgourmet

                Thank you for that info. I definitely didn't know about the soap & water effect on aluminum. How about my question regarding whether, or not, it's harmful to continue to use them or would buying replacements be a better way to go?

                1. re: goodhealthgourmet

                  Could you go into the science of this a bit more? I'm a physicist and your description sounds confuses me. A few web pages describe some kind of damage caused by hydrogen in very vague pseudo-science terms but it seems to me that what you're saying is that water + detergent + aluminum results in the production of a very strong acid (free H+ in solution). If it's strong enough to damage aluminum, wouldn't the OP's skin get ravaged?

                  I have some decades-old bare aluminum bakeware that slightly oxidizes if not used for some time, but I've never seen seen any flaking or immediate discoloration during or after washing. Same with a thick aluminum non-stick pan that has uncoated shiny edges.

                  Dishwashing liquid is slightly alkaline and the quality of water used could be an issue. My utility supplies water from the Sierra Nevadas that is very pure and neutral. The mineral content is a factor and if a water softener is used, I'm guessing that it causes the water to become alkaline. That combination will definitely corrode aluminum. One solution might be to switch to another dishwashing liquid that has better buffering (I've seen a type of Palmolive that's called "pH balanced")

                  1. re: PorkButt

                    See, oxidized is how I'd describe mine.


                    1. re: Davwud

                      Oxidized is what it is and aluminum oxide is pretty inert to my way of thinking. My contact with the oxidation of aluminum however is with the masts in several of our sailboats (yeah, I never ate off them-that is a given). Aluminum which is not anodized will necessarily oxidize but is it toxic, I think not. I brought an aluminum pot from my home to the new married state home and it had been used for 20 plus years, was pale chalky colored from years of use and cleaning. Nobody got sick - ever.

                    2. re: PorkButt

                      you answered your own question - as far as i know, it's a pH thing. the alkalinity of the soap + alkaline water = oxidation or corrosion. but what i *didn't* know is that there are pH balanced detergents on the market! that could definitely be helpful...

                      anyway if you have more detailed scientific information and a better explanation i'd certainly defer to you. i have several years of science education under my belt, but compared to a physicist i'm an ignoramus!

                      1. re: goodhealthgourmet

                        When I think about oxidation, it's either by the oxygen present in the air or hydroxide or peroxide molecules in a solution, not free hydrogen atoms. Aluminum oxide is a stable and inert mineral and doesn't pose a hazard. My guess is that some people are experiencing a gradual buildup that eventually powders off. To say that the aluminum is corroding is an overstatement because it would probably take more than a lifetime of daily washings to remove even a tiny amount of metal from the pan. Most restaurants use uncoated aluminum pans that are well maintained and stay shiny.

                        As an aside, Calphalon cookware is made of "anodized aluminum" which is simply aluminum that is subjected to an electrical current in the presence of a gas or solution that results in a hard and durable layer of - you guessed it - aluminum oxide!

                      2. re: PorkButt

                        I've experienced this before and also wondered about the cause. I came across a message board a while back and one poster offered this explanation:

                        "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. "


                        1. re: gmm

                          I don't understand that poster's reasoning at all. And for someone who claims knowledge of chemistry, to use the word soap for a detergent is sloppy.

                      3. re: goodhealthgourmet

                        Is it safe to ingest? I used the garlic press to make Guacamole and I hate to throw it out. There was just a tiny bit on part of the garlic as I stirred it in.

                      4. Does the OP cook with gas or electric? Is the residue on the exterior or the interior of the pot/pan? I cook with propane gas and have noticed a sometimes sticky residue on the exterior of my pots -- a good degreaser, a greenpad and some serious elbow grease takes care of it. I've been using Dawn and hot water to clean my pots for years, and while I've very occasionally noticed a flaky residue on the interior, I've never had a problem scrubbing it out. I always figured it was a residue from something I'd cooked before that was acidic.

                        2 Replies
                        1. re: chefbeth

                          WOW, I didn't expect this kind of response! PorkButt, you've increased my knowledge of oxidation exponentially! I cook with natural gas, and the residue on the pots and sheets is interior, on the garlic press, it's over the entire thing. One of the reasons for my question is that my wife is not in good health. She's on an organ transplant list, recently developed breast cancer (the same day being diagnosed with shingles on the other breast!) and generally is not well. I wanted to make sure that the condition of my cookware was not going to exacerbate her conditions.

                          1. re: bucksguy14

                            Not to put too fine a point on it, but wouldn't that be better discussed with a medical professional rather than culinary amateurs?

                        2. Send them my way and I will dispose of them immediately!

                          1. Just a crazy thought -- but could it be hard water or mineral residue? This frequently happens INSIDE kettles and pot, but aluminum is usually not quite a polished. Have you tried soaking it in a white vinegar solution for just a few minutes (not too long to hurt it)?

                            1. Discovered that the reason the residue was showing up on my pans was that I had been using a heavy-duty (green & yellow) sponge to clean them. I ran out of those and couldn't find the same thing at Costco, where I'd been buying them, so I bought what was available (dark blue over lighter blue). Starting using those about a month ago and no more residue! I had a second post on this and received an answer that the new sponges were not releasing the residue and that's why I'm not seeing it anymore.

                              4 Replies
                              1. re: bucksguy14

                                When you say residue, do you really mean something that can flake off or is it more of a discoloration? If you boil potatoes in an aluminum kettle the water will discolor the kettle. Simmering water with an acid such as lemon juice or vinegar will remove the discoloring. We have a nylon cutting board that was stained by carrots so I washed it and put in on an aluminum 1/2 sheet pan and pour some bleach on the cutting board. The cutting board came out white, but the 1/2 sheet pan got discolored. I washed it and it's fine, but still looks a little funny. There was a change in the appearance but no residue.

                                1. re: John E.

                                  John E., there is no flaking. There is a little discoloration but the thing that concerned me was a gray residue, like a film, on my towel when I dried the pans. The discoloration has been eliminated by the use of the new blue/blue sponge.

                                2. re: bucksguy14

                                  The heavy duty (green and yellow) sponge is more abrasive than the blue/blue. What you've been seeing over time is the abrasive sponge wearing down your aluminum. Continue using the blue/blue sponges and you won't have a problem. I only use the green scrubbie when there is major league stuff on my pans. Typically, the blue/blue takes care of everything.

                                  If you want a product to clean those pans that's not terribly abrasive but will get the job done, try using Bar Keeper's Friend or Cameo Aluminum/Stainless cleaner.

                                  I have a TON of aluminum cookware (anodized and non-anodized) and have been using the blue/blue sponge along with Cameo for years (15+). My pans are clean and we have no health problems.

                                  1. re: Dee S

                                    Thanks, Dee. I'll look for Cameo and give it a try.