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1·Redd cloud nigrescence cloud, there is rain on.

红云变黑云，必有大雨淋。

2·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.

本文讨论了诸多因素对黑化速度及黑化膜性能的影响，确定较好的常温快速化学发黑实用技术。

发黑

1·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.

本文讨论了诸多因素对黑化速度及黑化膜性能的影响，确定较好的常温快速化学发黑实用技术。