Fake stainless steel?

[Mastoras007]

Hello.
I left the beer tap inside the star for a few days (3-4).
I had opened it in pieces and left it inside until it was time to use it again.
when I took it out I saw that some of the parts which before I put them in were stainless steel changed color.
Any idea?

 

[Minbari]

If i had to guess, the back pieces are lower grade stainless. Maybe higher nickle content and reacted with the acid

 

[Donoroto]

I am guessing they were chrome-plated brass. Polish them nice and don't leave them in acid again.