"People can feel nigrescence but it's not obvious. “能感到变黑的感觉，但不是很明显。
What to do if the silvered jewelry become nigrescence(black color)? 银饰发黑怎么办？
But the sky sudden nigrescence, has combined at least 30 minutes rainstorms. 但天空突然变黑了，并下了至少30分钟的暴雨。
When Dao is baked,it is nigrescence at first,and then blanched.But this diferent from wrapped steel. 烧刃线磨时先是发黑，继续磨后发白，但白得和夹钢的发亮不同。
With regards to the surface treatment, our crafts include nigrescence, phosphorization, zinc plating, dacromet, nickel plating and copper plating. 表面处理有发黑、磷化、机械镀锌、达克罗、镀镍、镀铜等工艺。
First, strengthens against exposes to the sun, against exposes to the sun can complete can prevent the cheek nigrescence. 第一、加强防晒，防晒做得好就能预防脸蛋变黑。
