Zincs are composed of an alloy that meets Mil-Spec MIL-A-18001 for sacrificial anodes. This alloy is mostly zinc, but with measurable concentrations of cadmium (~0.1%)and aluminum (~0.25%). The additional cadmium causes the anode to erode from the surface inward, which causes a ''sandblasted'' appearance to the surface. When the anode is almost dissolved, it needs to be replaced.

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