This first layer of dense molecular nickel is deposited to the wheel to protect against galvanic corrosion. This will almost always happen when two electrochemically dissimilar metals are in contact for extended periods of time. This semi-bright nickel layer acts as a shield to the wheel to keep corrosive forces from penetrating the base material.

This layer is the principle reason why today's high quality chrome plating will far outlast plating of the past.

Platers that skip this layer often have product that peels prematurely, or worse yet, could create a dangerous driving condition if the wheel base material begins to corrode.