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What is happening with my aluminum baking tray? - stainless steel over heated black

When I recorded with liquid oil, spray, butter or Crisco, then the excess wire with a towel, I have a black residue? Why?
If the oil react with aluminum? And that is dangerous?
In what does the candy to make them learn in the rule of using stainless steel, but he asked himself, IV, covering 10 different restaurant supply houses, and to say that the large stainless steel bowls with thick, almost extinct, and if you have a to find their 200bucks. I am currently working with a stainless steel tray to steam buffet. But this indicator is very thin and get all distorted by heat, microphones, if it is very difficult to work the sugar. Therefore, I would like to use on aluminum, but I need to know what the waste?
Ideas?
Aluminum is cool when the temperature of waste before Pour candy and it's clean! Or left unburned oil.
not a plateau age
Thank you very much for all the help, but their thinking about something else is the bowl is new, clean, without residues Pryor? Cool, put a little oil in it, clean the oil and see things in black and Exss twoel not seem professional, oil in the pan yet clear on this point. And the towel is not dirty, I have tried different paper and paper towels. Another thing, what is happening here?