Error collectors quite rightly get excited when they sweep a magnet over a pile of U.S. coins and one of the coins sticks to it. The only domestic coins that should stick to a magnet are the 1943 Lincoln zinc-coated steel cents.
Only two metallic elements commonly used in coinage will be attracted to a magnet — iron and nickel. Coins composed of iron or steel will slam into a magnet, as will coins made of pure, elemental nickel.
Violent attraction to a magnet may indicate the presence of a foreign planchet. That’s certainly the case with the illustrated 2001-P Jefferson 5-cent coin. This full-diameter coin is quite underweight at 3.33 grams (a normal 5-cent coin weighs 5 grams).
The coin is covered with a thick, glossy black cortex that is quite friable. The cortex may have formed as an oxidation product when the blank was annealed at temperatures appropriate for normal 5-cent coins. Certainly no conventional world coin has a surface like this. The cortex has flaked away around the perimeter and elsewhere, revealing underlying gray steel. Some rust spots have developed on the exposed steel.
This is the third steel Jefferson 5-cent coin I have encountered that was struck during this time period. The other two were undersized (both underweight and too small in diameter).
All three “orphan” off-metal errors probably trace their origin to the Royal Canadian Mint, which supplemented the U.S. Mint’s supply of 5-cent blanks during the years 1999 to 2001. Canada strikes coins for many countries, so it’s not surprising that a foreign blank would occasionally get mixed in with a batch of 5-cent blanks heading across the border.
A weak attraction to a magnet in a coin that should have no attraction is more problematical. It can be caused by the presence of iron-rich slag, as in the 1979 cent described in the Dec. 14, 2009, column. Embedded pieces of steel or pure, elemental nickel will also generate a magnetic pull. Metallic debris can embed itself in coin metal at many points in the production stream. It can fall into the crucible or molten ingot and it can get rolled into the strip, be forced in by the blanking die, be squeezed in by the upsetting mill or struck in by the dies. But in all these cases, the foreign matter will be visible on the surface or will at least alter the coin’s surface appearance.
A weak magnetic attraction could also indicate an improper alloy mix involving an unusually large amount of nickel in a solid copper-nickel coin. That said, I’m not sure how high a percentage of nickel is necessary to generate a magnetic pull or if the transition from nonmagnetic to magnetic is gradual or abrupt.
In most cases, a weak magnetic attraction indicates you’re dealing with an altered coin or even a counterfeit. The most common cause of a weak magnetic attraction is nickel plating. Double-plated coins that consist of an inner layer of nickel and an outer layer of some other metal will also create a weak magnetic pull.
Recently Jim Ciccone sent me a 1987-D Lincoln cent that is weakly attracted to a magnet. He was hoping it was an off-metal error but it turned out to be a double-plated cent. The coin is gold-colored with an unnatural gleam. It’s also slightly overweight at 2.6 grams. A normal cent weighs 2.5 grams, so the slight increase in weight is consistent with added plating. But be aware that plated coins can have a perfectly normal weight or even be underweight. Before plating, a coin has to be chemically cleaned, and this process, if taken too far, can strip enough of the surface metal away to leave the coin underweight, even after plating.
The gold surface plating is quite thin and has worn through in spots to reveal bright, white metal that is almost certainly elemental nickel. Beneath that, I suspect you’ll find the original copper plating and, below that, the zinc core. I have no doubt that this is a zinc cent, because small plating blisters are visible despite the added plating and because the pattern of die deterioration is characteristic of zinc cents.
Magic shops are happy to sell you magnetic coins. These sometimes end up in dealer showcases. Such trick coins are produced by drilling a hole through the edge of a coin or slicing into the edge with a fine saw blade. The resulting aperture is then filled with a rod, pellet, or wafer of steel or with a magnet. The gap in the edge is then sealed up and plated over.
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