I just bought some hard-anodized aluminum pots. The instructions specify to not wash them in the dishwasher. Why is that? The instructions say that you can use Comet, Scotch-Brite, etc. by hand, but they say there’s something harmful about the detergent that’s used in the dishwasher. If it’s so bad then why can I wash plates in it?
Well metals and ceramics have different chemical resistance properties. Now that I have exhausted my techincal knowledge of the situation I’ll offer an anecdote. I have a couple of baking pans that seemed brand new, until the Missus and I improved our situation with a dishwaher. Now they seem to be oxidizing at an very fast rate.
Hopefully someone who can address the specific whys will be along shortly.
rainy
I think the issue comes down to acidity, not resistance to abrasives.
Anondized aluminum will get worn by acids. I’m making a jump to the conclusion that dishwasher soap is acidic, esp in light of the fact that many use citric acid (lemon boosted this or that, etc, etc).
So, it makes perfect sense that the instructions say to scrub with cleanser (as I do for my wife’s anodized aluminum), and it makes sense that you don’t want those dishwasher chems attacking it with acid.
Abrasives — anodized alum is tough
Acids – anodized alum ain’t so tuff over time… Alum layer could wear, etc
Actually on anodizing, aluminum oxide, I think the danger is bases more than acids as most dishwashing detergents are moderately basic. I’ve never seen an acidic soap. This is one disadvantage because a strong base like oven cleaner is the best thing for stripping polymerized oils but will strip anodizing in a hillbilly’s heartbeat. This is sometimes a problem in rifle shooting where ammonia cleaners are used to clean copper fouling from barrel bores. It works great on that but will etch the hard anodized finish on an AR-15 reciever. I’m sure strong enough acids will harm anodizing too but I’ve never had problems with my Calphalon with the PH levels in tomatoes or vinegar.
I never put carbon steel in the dishwasher becuase slow, evaporation drying accelerates rusing so badly.
I would like to revise my comments to say that it is definitely a pH issue. ! Did I say acid?
…Because anodized aluminum is fine for cooking acidic foods, and 'cause my wife said so, and cause Padeye makes sense.
I know aluminum in the presence of baking soda causes an oxidation/reduction reaction. This is what you do to clean silver-place tarnished silver in a solution of baking soda in an aluminum pan or container with aluminum foil and the tanish disappears.