Petromax HK250 restoration

The black spots are: rust, "blank" metal.
You will not get the shiny new look back with any treatment, I am afraid ;-)

There is also no easy, speedy, wonder stuff that gets an old lantern clean again. It's all to elbow spit and lame hands from polishing.
For electro plating the metal must be clean, spotless and it will not remove dents and/or pitting.

 

If they are rust as you say, why a rust remover or even better a rust converter (like tannic acid) will not stop the corrosion? My issue is not to make it shiny again. I understand that this is not possible anymore. My target is to stop or slow down corrosion. For example, tannic acid turns rusty metals to black. I have no problem with this. Let it be black. Will corrosion stop? Or prevented?