[gargarean]

Dear friends, good day.

Please help me with the following chemical riddle!

I do some homebrewing.

I use a Sodium Bicarbonate solution (NaHCO₃ in water) to take labels out easily, leave bottles in the solution for some hours then labels just float up.

I have a large aluminum pot to boil the wort in, to be soon replaced by a stainless steel one.

I had the (bad) idea of using my pot as a receptacle to soak the bottles in the NaHCO₃ solution. As I had many bottles to treat I was replacing the ready ones with labeled ones and to make a long story short left the solution in the pot for about a week. After I drained the water I found out to my dismay that the aluminum surface has been covered by a black layer.

I tried to take it out mechanically (scrubbing) but it goes off very slowly and painstakingly. I also tried scrubbing it with weak acid (lemon) but didn't see any big difference.

I was wondering whether I could just fill the pot with ANOTHER solution and leave it overnight and it will just have disappeared in the morning and pot will be shining again!

I had a thought that maybe Al replaced Na in the baking soda and the black stuff is Al(HCO₃)₃, even tried to find if Aluminum Bicarbonate is black but had no luck with google. And probably it's a stupid idea since Al is more electronegative than Na? Or is it Al(OH)₃? But that one seems to be white as per google...

I hope somebody can help with this. Sorry for the long post.

Thank you very much.

[Hunter2]

Aluminium will be dissolved in alcaline and acidic solutions. Also baking soda will attack the aluminium. So not a good idea to use a aluminium pot for that. The pot is probaböy made of an alloy, what left the black material.

[Enthalpy]

The black layer may well be much more resistant to chemicals than aluminium is. What about using a rotating hard brush powered by a drill?

[billnotgatez]

http://www.ehow.com/how_8595865_black-out-aluminum-pot.html
maybe this link

They suggest using
2 tbsp. cream of tartar
Spoon
4 tsp. white vinegar
Dishwashing detergent
Nylon mesh scrubber
Kitchen towel
Silver polish
Clean cloths