Neutral Salt Spray Testing

 When zinc corrodes, it develops a white powdery product on the surface, prior to the appearance of red rust
on steel. To delay the appearance of this “white rust” on zinc plating, a chromate surface treatment is applied.
This chromate film seals the surface to increase the corrosion protection of the zinc. 
The corrosion protection of the zinc coating  can be measured by Salt Spray Hours. Salt Spray corrosion testing
as per ASTM B117 is performed in a controlled test chamber with continuous exposure to an atomized fog of salt solution.
Salt spray test results provide a method of comparison testing of coatings in a controlled environment, but may not
directly predict corrosion protection in real world conditions.
There are Australian and Industry standards for specific minimum salt spray testing requirements 
for the finish, thickness of the coating.