Here in Brazil we use a special detergent to clean up metals, based on Dodecylbenzene Sulphonic Acid, it is very effective at shining up all sorts of different metals.
I recently acquired 2 samples of 99.99% pure metallic cobalt for my element collection... They were covered in some sort of weird blackish-grey-green-brown residue...
I then dumped the 2 pieces of Co in a small container with this special dish detergent... to my surprise, this blackish residue immediatelly started to come off. After some time, I was left with very shiny pieces of Cobalt.
Did some reaction actually take place here? What reaction? Thanks in advance. As I understand, Cobalt is meant to be rather resistant to acids/corrosion in general.