The U.S. Copper Penny is actually composed of 97.5% zinc and only a thin copper coating.
Reference: U.S. Mint
As a final step in the galvanizing process, the hot-dip galvanized coating is inspected for compliance with specifications. Interpretation of inspection results should be made with a clear understanding of the causes of the various conditions which may be encountered and their effects on the ultimate objective of providing corrosion protection. Inspection of the galvanized product, as the final step in the process, can be most effectively and efficiently conducted at the galvanizer’s plant where questions can be asked and answered quickly.
The service life of galvanized steel is directly related to the thickness of the protective zinc coating. Corrosion protection is greatest when the coating is thickest. The coating thickness is the single most important inspection check to determine a galvanized coating’s quality. There are a number of simple magnetic gauges that can be used to give a convenient and reliable measurement of the zinc coating thickness, provided the instruments are properly calibrated.
Coating thickness, however, is only one inspection area. The coating’s uniformity, adherence, and appearance should also be checked. For the most part, galvanized coatings lend themselves easily and most effectively to simple visual inspections. There is a saying in the galvanizing industry, “If a galvanized coating APPEARS sound and continuous, it IS sound and continuous”. This adage refers to the characteristic properties of a galvanized coating and the simple fact that if a steel or iron surface is not prepared properly, a galvanized coating will not form. Uncoated portions of a material’s surface will appear as dark, black areas and be easily distinguishable from the surrounding gray or silver galvanized coating.
The American Galvanizers Association has a variety of free resources that are available detailing the procedures and points to note when performing inspections of hot-dip galvanized coatings. The most relevant are linked below: