Okay so recently, I gifted my friend this good quality fake gold pendant inside a small gift box. She kept the gift box with her the entire day in her bag which she carried around with her and only tried it on once without taking the tag off. Now when she got home, when she opened the gift box again once she got home, half of the gold chain had turned silver, according to her. She showed it to me today and I asked her if she did something, like take in water or you know the usual jewellery stuff and she didn't. It was expensive so I can get it changed from the store but I want to be sure of the cause so I know whether it was the store's fault or if something happened to the necklace itself by being in the box. So anyone have idea what could've happened?Okay so recently, I gifted my friend this good quality fake gold pendant inside a small gift box. She kept the gift box with her the entire day in her bag which she carried around with her and only tried it on once without taking the tag off. Now when she got home, when she opened the gift box again once she got home, half of the gold chain had turned silver, according to her. She showed it to me today and I asked her if she did something, like take in water or you know the usual jewellery stuff and she didn't. It was expensive so I can get it changed from the store but I want to be sure of the cause so I know whether it was the store's fault or if something happened to the necklace itself by being in the box. So anyone have idea what could've happened?

Maybe a chemical reaction with one of the minerals in the fake chain

fake gold necklace changed into silver it is possible as the gold plating done on the metal doesn't stay permanently for longer time.