| a) | Conditions at the cut. When the product is cut, the cross section shows coat-drooped part and exposed-substrate part. |
| b) | Conditions in an early period. As zinc in the coating layer of the product provides sacrificial corrosion to protect the substrate, red rust (Fe oxide) develops on exposed-substrate part if it gets wet with rain or some other water in early stages of installation. |
| c) | Exhaustion of Zn in the coating layer near the cut end and development of red rust on the cut end. |
| d) | Conditions after certain years. Corrosive growth of Al, Zn, S and O develops over red rust some years after installation and such growth works to suppress corrosion of the coating layer and substrate. |
