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Lecture 4 - Copper and the penny

Listen to part of a lecture in a materials science class.

Professor: So what’s the first thing that comes to mind when we talk about uses for copper? Tammy?

Student: The penny. It’s made of copper.

Professor: Okay, good one. But what’s a one cent coin worth these days? You might get back change. Like if you go to the store and give the cashier 5 dollars for something that costs 4 dollars 98 cents, you’ll get 2 cents back, but 2 cents does not buy much. The value of the penny in terms of what it’ll buy has gotten so low that there’s actually a move afoot to eliminate the coin from US currency. But there’s more to it.

As Tammy implied, the penny looks like it’s solid copper. It is reddish orange with a bright metallic luster when it’s new, but that’s just the copper plating. The penny’s not solid copper. In actuality, it is almost 98 percent zinc.

But given the rising value of both these metals, each penny now costs about 1.7 cents to produce. So it generates what is called negative Seigniorage.

Negative seigniorage is when the cost of minting a coin is more than the coin’s face value. Even though the penny generates quite a bit of negative seigniorage, there is concern that if it’s eliminated, we’ll need more nickels, because more merchants might start setting prices in five-cent increments, 4 dollars 95 cents and so on. So we need a trusty five-cent piece that can be minted economically. But the nickel’s negative seigniorage is even worse than the pennies. Each nickel costs the US mint 10 cents to produce.

Also, some of us are pretty attached to pennies for whatever reason, nostalgia, and then those collectors. And people, if they see a penny on the sidewalk, they’ll pick it up and think: it is my lucky day!

Another scenario is that, without pennies, merchants, instead of charging 4.98, might round up the price to an even five dollars. So consumer goods would become slightly more expensive. But on the other hand, some cash transactions would be more convenient for consumers. And as I said, the government would save money if pennies were eliminated.

Student: But wouldn’t the copper industry suffer financially if the US government stopped buying copper to make pennies?

Professor: But how much copper do pennies actually contain?

Student: How much…Oh/ got it, right.

Professor: So what else comes to mind when you think about copper? What else is copper used for?

Student: I know that copper can be shaped into all sorts of things:sheets, tubing, and my cousin’s house has a copper roof.

Professor: Yes, like gold and silver, copper is extremely malleable, but it’s not a precious metal, it’s far less expensive than gold or silver. It’s also a superb conductor of electricity so you can stretch it into wires which go into appliances and even car motors.

Copper also has superior alloying properties, it’s…you know, when it’s combined with other metals.

For instance, how many of you play a brass instrument, like a trumpet or a trombone?

Well, brass is an alloy of copper and zinc. If your trombone was made of pure copper or pure zinc, it wouldn’t sound nearly as beautiful as a brass trombone.

Another alloy, a combination of copper and nickel, resists corrosion. It does not rust, even with prolonged exposure to water.

Student: But what about the Statue of Liberty in New York Harbor? It’s made of pure copper, but it turned green. Isn’t that a sign of corrosion?

Professor: Indirectly. If copper’s exposed to damp air, its color changes from reddish orange to reddish brown.

But in time, a green film, called a patina, forms and the patina actually serves to halt any further corrosion. It is one reason that ship hulls are made of copper-nickel alloys. These alloys are also hard for the barnacles to stick to. If these little shellfish adhere to the hull of a ship, it produces drag, slowing the vessel down.

Copper’s also a key material used in solar heating units and in water desalination plants, which will play increasingly important roles in society.

Bottom line: if you are a copper miner, you won’t lose any sleep should the penny get. If you’ll excuse the expression, pinched out of existence.