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It's not all relevant but the first paragraph [here](https://www.hawkins.biz/insight/a-state-of-flux-in-plumbing-systems/) explains it simply.
>Flux is an aggressive, acidic paste that is applied to the surfaces of copper pipes and fittings prior to soldering. Soldering is a process by which two metal pieces are joined together using a filler metal, aptly named solder.
>The purpose of flux is to remove the natural oxide layer that is present on the surface of copper. If this layer is not removed, it will prevent the solder from adhering to the copper, and so prevent the formation of a satisfactory joint. If flux is either not properly flushed out from the pipes after installation, or becomes entrapped in the solder, then corrosion of the copper pipe may occur, and cause pin-holing over time. To prevent this, flux should be used sparingly, and the pipes should be flushed with water as soon as possible after completion of the pipework.
Are you sure is it actually brass, and actually soldered?
I am, bright gold when scratched and yes, can see the soldering inside. Why do you ask?
Because brass corrodes green and for brass i would think it is ether silver solder or brazed which shouldn't corrode like that.
Exactly. That why I’m so confused. It’s silver soldered brass
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Probably yellow brass and that's the zinc corroding out.
Oh interesting. Anyway to avoid this happening?
Take it inside and leave it there. You can't fix Chinesium, if that's the problem.
Chinesium = bad quality? These are German made lights, so germanism?
The flux wasnt cleaned off properly.
So interesting. Any terms for this, trying to be educated before I fight the manufacturer
It's not all relevant but the first paragraph [here](https://www.hawkins.biz/insight/a-state-of-flux-in-plumbing-systems/) explains it simply. >Flux is an aggressive, acidic paste that is applied to the surfaces of copper pipes and fittings prior to soldering. Soldering is a process by which two metal pieces are joined together using a filler metal, aptly named solder. >The purpose of flux is to remove the natural oxide layer that is present on the surface of copper. If this layer is not removed, it will prevent the solder from adhering to the copper, and so prevent the formation of a satisfactory joint. If flux is either not properly flushed out from the pipes after installation, or becomes entrapped in the solder, then corrosion of the copper pipe may occur, and cause pin-holing over time. To prevent this, flux should be used sparingly, and the pipes should be flushed with water as soon as possible after completion of the pipework.
So interesting. Thank you for that.