1. The thickness of the surface coating is different, the surface coating of black zinc plating will be thicker than the black one. Black zinc plating is an electrophoresis process. After the power is turned on, the electroplating medium in the solution will adhere to the non-standard screw, and the thickness of the coating is about 3-2Oum. Blackening is the chemical change of the data of the non-standard screw itself, which will oxidize the surface data of the screw into a passivation film. The thickness of the passive layer is typically about 3um.

2. The phenomenon after soaking in acid is different. Soak in acid. If the black layer recedes and there is a white layer and continues to react with the acid, it means that it is passivated black zinc, otherwise it will be black.

3. The phenomenon caused by scratching on it with white paper is different. Take a piece of white paper and scratch it hard, and the blackened one will fade, but the black zinc-plated one will not.

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