The original white lead pigments have oxidized and turned black.
原来白色的铅颜料已经氧化发黑了。
《柯林斯英汉双解大词典》
2
Green tea contains between 30 and 40 per cent of water-extractable polyphenols, while black tea (green tea that has been oxidized by fermentation) contains between 3 and 10 per cent.
绿茶含有30%——40%的可以水萃取的茶多酚，而红茶(绿茶经过发酵后的产物)只含有3%——10%。
3
Black liquor is a water slurry containing both organics, which are oxidized and inorganics, which are recovered as pellets.