Metals are commonly coated with other metals, either with thermal spraying (metalizing) or hot dip galvanizing. The coating metal in galvanization is zinc. Hot dip application of zinc is very robust with several layers created by alloying of zinc with the base metal, in this case steel. In the other two images some cracks are visible starting from the outer surface. Since these cracks formed during or before the galvanization process, the inside surface of the cracks is also coated with zinc.