Goodmorning,
as stated here I am into the process of opening a website about Italian public lighting where I will show what I have salvaged so far and what I plan to do in the future.
This means, obviously, that I have to begin to restore all of the fixtures I salvaged in these 6 years (~600, 2x type) that, for the moment, have been stocked into a building.

Some of the fixtures I salvaged, are covered both inside and outside in a black layer of "something", which I believe it to be smog.

Currently I am trying to use both anti-limescale and Chante Clair (yep! the grease removal thing) products and while this thing is good to remove dirt, dead animals and some oxides, is totaly unable to remove the black layer unless I scrub a lot with the green part of a dish-washing sponge and still not being able to make it go away completely (Also, this operation cannot be done on reflectors as it damages the surface leaving scratches).

I then resigned to buy a specific anti-smog product, which is called "No Smog", that contains a solution of sodium hydroxide (UN 1824, basically caustic soda) but I don't see any difference, still needing to scrub a lot to get rid of the black layer.

So, being on a lighting forum, with many lighting fan users that have in their collection many fixtures I am wondering if some of you got the same problem and somehow did manage to solve it.

Thanks to everyone.