Could it be soap residue or hard water residue? Either way one of these usually works:
1: Vinegar:water,1:2 ratio with a squirt of liquid dish soap (not dishwasher soap). Place in pot and heat to almost a simmer. Place stuff inside pot and let that marinade for a few mins, try to rub with a cloth or sponge. If that doesnt work then...
2.CLR. BUT you would want to do a teeny tiny patch test first.

Thats all I can think of, Im sure there will be a lot of other awesome suggestions.

try bar keeps friend

make a paste with some of the powder and a little water, use a paper towel (in my experience, it does best with paper towels)

if that doesn't work, nothing will.

best of luck!

sidenote - you should be able to find it in the cleaning aisle of the grocery store, or, if they don't have it - any hardware shop will do

Buy your neighbor a new one STAT! Then you can experiment with cleaning this one up for yourself. I definitely don't advise using harsh chemical products like CLR on a kitchen item that you've borrowed from a friend.

I ran a Bodum stovetop espresso maker through the dishwasher once, and the finish was never the same.

Explain what happened to your neighbor, and buy them a new one STAT.

Try cleaning this one up for yourself. Who cares if it's not pretty as long as it still works.

Lemon juice sometimes restores metal finishes. If that doesn't work, buy them a new one.

That's galvanic corrosion you're looking at, and it's not going to scrub off. The aluminum of the Bialetti pot reacted with the conditions in your dishwasher, and chemistry happened. But your friend a new pot.

Lanea, exactly. The conditions inside a dishwasher are very corrosive, it takes strong detergents to remove food without scrubbing.

You need to buy a new one... sorry... my wife did this to mine, I tried every aluminum product known to man and it didn't work.

You "broke" it you bought it. Buy a new one for your neighbor and suck it up.

Why even ask how to clean it? You owe your neighbor a new pot! No question!!!

I am always amazed when people borrow things thinking it's OK to return them in anything less than the condition they borrowed them in. Truly amazing.

JROSSI, why be unnecessarily rude? The asker mentions it was not the brightest move, obviously. No need to make them feel worse about it. And honestly, if you would be pissed about something as simple as a patina on a coffee pot, you need to reevaluate your neighborly intentions. Glad we don't live next door to one another.

Wow, you guys, the person's trying to make it right. How about being helpful instead of making them feel worse than they already do? I'd assume if it can't be cleaned the person will replace it.
Also, I never loan anything I can't do without. Saves a lot of hurt feelings and heartache.

I sell these products here in Montreal and I have never been able to return one to its original state. Anything aluminium cannot be placed in a dishwasher.

Talk to them, apologize, replace the pot with a new one of the same make and model unless they specify otherwise. It would be a good idea to apply a little salve too - find out what kind of coffee they drink and buy them a generous amount.

buy your neighbor a new one, and apologize profusely.

as for this one, i'd forego the barkeeper's friend (and as a lover of anodized aluminum cookware, i am never w/o the stuff) and make a paste out of baking soda and water to try on your new bialetti.

I did this once as well.. I was pretty upset at myself after doing it. I ended up having to toss it out, as I couldn't remedy the issue. I'm sure if you're honest with your neighbor about it, they'll understand. Maybe buy them a new one or offer to give them money to pick out your own? Good luck!

Order a new one now and experiment on your new gadget.

A) Replace this one with a new one to give to your friend.
B) Clean this one with Bon Ami and enjoy it.

My mom did the same thing to mine but it cleaned up very well with Bon Ami.

I would just like to say mistakes happen. Ignore the haters and be thankful they are not your neighbor! For Heaven's sake, they mass produce these pots! Geez! Lighten up, people & go fix yourself a cup of coffee.

I was never able to restore aluminum from this condition either-- I was gifted Magnalite pans that had gone through the dishwasher. I would also buy a replacement for your neighbor but NOT apologize profusely or feel badly about your learning curve! Your intentions are honest & good.

My sister in law put my family's antique hand carved bone-handled carving set in the dishwasher and it was 'ruined'. She felt so badly. These things happen. Oh well! She's still my sister in law and there is no question who I love more (her, btw). It's all just 'stuff' in the end. Relationships are what people who matter will remember.

Ooo, Bon Ami...will try this on my Magnalite pan...

thanks for all the actual cleaning advice, Kitchn peeps! Not really looking for etiquette advice - I'm a grownup (most of the time! ha) so I can take care of that part myself. Also thanks Kitchn for the other link! lots of good info there...
~sue

Tj Maxx and Marshalls seem to always have these much cheaper than the kitchen stores. Look there first before you pay a bunch.

That thing costs $20. Buy them a new one.

Hey ROCAKLITA-Sue - if you're feeling adventurous, one you buy your friends a new pot, take your inherited coffee maker and try this:

http://www.instructables.com/id/Electrolytic-Rust-Removal-aka-Magic/

I realize the corrosion may not respond the same way as oxidation, but it might be fun to try.

@ sue - what a REFRESHING (grown up) response
did ma heart good =]

You can try with water, white vinegar and baking soda. By the way, I never ever clean my moka with anything but water. Here in Italy we use those stuff on a daily basis and it takes a bit of time to come out with a good flavour: so, if you need to buy a new one to your neighboors, you can also buy a couple of packs of coffee and do as many coffees as you can. That's what I do when I need to buy a new one and it usually works. Good luck!

One thing always worked to shine the metal surface is tooth powder. You need to buff it with cotton cloth and not a easy job. You can use toothbrush for hard to reach areas with tooth powder dipped in. It does the same job as buffing paste (available in hardware stores) so alternately you can use them. Not to forget, thorough cleaning is necessary both before and after buffing.

Oh well. It's happened! Unfortunately you may just have to find a replacement.

I arrived here while searching for an answer in how to restore the shine in my Bialetti stove top coffee maker. The first mistake was to use and abrasive powder. Then after reading here some of the comments I used polishing compound wax. It does a good job and the coffee maker looked a lot better, but I wasn't happy with the results. A few days later I polished it again with liquid metal polish and it worked!! The pot looks shiny again.

Hopefully this helps some else in the same situation.

I know it may be too late but you can polish aluminum and other metal items with jewelers rouge. Google "jewelers rouge dremel" or just jewelers rouge on youtube for tips. Steer clear of the ones with large power tools which most don't have on hand and aren't polishing an entire mack truck big rig! http://youtu.be/Asd7GAio00s

-------------------------------------ALL IS NOT LOST!!!------------------------------------

My flatmate put the top half of mine in the dishwasher, It looked awful as described above. Having read this i thought there was no hope. I used Autoglym metal polish. I'm not exagerating when i say it is now literally as good as new. I can tell because the bottom half was spared the dishwasher and side by side there is no difference in colour or finish.

One of my room mates accidentally put my bialetti coffee maker in the dishwasher... Is it still safe to use once its become corroded?