Do you cook your food in it or just place jars of food in it.

Both. We will often use it to make a large batch of soup stock

Try the Cooking forum. Those people are wizards!

Please don't cook in an aluminum pan/pot. It causes Alzheimers. Years ago they autopsied AZ patients and found far to much aluminum in their brains. A week later they retracted the statement and said the aluminum was cause by the AZ. Now if you believe the human brain can manufacture alum I have bridge to sell you. They were probably lobbied by the aluminum cook ware companies to do that so they could unload their existing stock. Now you can't find any aluminum cook ware unless it has a lining in it. The AZ organization always believed it was caused by aluminum. Now they have grudgingly said "maybe" it is not the cause. I google every prescription the doctor prescribes for me. One med for my stomach put up an alert saying, "seniors, this med will add to the accumulation of aluminum already in your body".

Boil tomatoes & water in the canner. The acid will reduce the tarnish. Boil long enough and the pot may end up being completely clean of tarnish.

Vinegar might serve the same purpose. It is the acid that does the trick.

I personally changed to a stainless steel pot for cooking and use the aluminum one only for processing jars of food.

Go 2 the store and buy 5 or 6 cans of Creme of Tartar. Bring it 2 a boil and turn it down until U have a simmer. This will take 4, 2, 5 hours. Use the lid and B certain 2 check the water level, as it does evaporate. The black will B gone.

Based on the description of what it looks like and the controversy about aluminum, I'd continue using it but only for water-bath canning with glass jars. I wouldn't use it for actual food preparation. Consider tossing/recycling it and ask for a new one for Christmas.