[debun]

So I live in GA and the clay stains everything.   I have an abused dirt bike that I purchased off CL that I would like to restore.   The aluminum engine cases, wheels, radiator etc are badly oxidized and clay stained.  I have been experimenting with various cleaners and heard Sodium Hydroxide can be used to strip anodization/oxidation.  NaOH is damn near impossible to find locally so I purchased some Drain out, drain opener  http://www.summitbrands.com/summit/downloads/msds/usa/MSDS%20Drain%20Out%20Crystal.pdf and mixed a dilute solution and tested it a shifter that was likely forged or permanent mold cast and got a strange reaction.  The question is what is this black substance?  Is it one of the alloying agents in the AL?  A reaction with one of the other ingredients in the drain opener?  Does anyone know of any other household chemicals I could use to etch the aluminum alloy parts,and leave them natural in color? 

1) Very dilute and after about 15 minutes formed a black residue on the test part that could be scrubbed off.  The dotted line is the depth I dipped it too and you can see the portion I scrubbed with a scotch bright.  (Click on pic to make bigger)


2) A more concentrated solution after about 1 minutes formed the same black residue  but more difficult to remove. (Click on pic to make bigger)