1. After each time roll changing, must inspect the lubricant whether to harden the nigrescence , whether by impurity pollution, whether to oxidize the emulsification.

2. This is you from seashore insolation return period of time, not only long spot and nigrescence , moreover the very long time with difficulty restores reason.

3. First, strengthens against exposes to the sun, against exposes to the sun can complete can prevent the cheek nigrescence .

4. This paper work out a better applied technique of steel normal-temperature quick nigrescence via discussing various factors' influence on the speed of nigrescence and the capability of plating.

5. With regards to the surface treatment, our crafts include nigrescence , phosphorization, zinc plating, dacromet, nickel plating and copper plating.