Làm 925 chuyển màu bạc?
Đúng,oxidation with alloys that lend it the hardness and also with silver changes colour at the surface level.the look or effect is aesthetically liked by many ppeople.
It can be done under controlled environment too,for desired effect.
Chưa,if you want to avoid it,please get that silver electro coated, else there is a varnish like transparent liquid thats applied to prevent contact with moisture and air.