Why Do Pennies Turn Brown?

Are you interested in science, and have you ever wondered why do pennies turn brown? Pennies have been a form of currency for centuries. In fact, pennies were introduced in England before the thirteenth century. Over time, pennies have changed, and obviously they do not hold the same value in each country. In the United States, the value of a penny is one hundredth of a dollar. The composition of the coin has changed over time as well, and this helps answer the question of why do pennies turn brown?

Why do pennies turn brown? When you receive a new penny, you will note how shiny it is. This is because of the thin copper layer over the zinc, which gives the penny a shiny exterior.

The thin layer of copper is actually a copper alloy. Over time, your pennies turn brown because they are reacting with the air. The process that occurs is called oxidation.

Oxidation occurs when oxygen is added to a compound, usually by reducing the amount of electrons in that compound. You see the effects of oxidation frequently in your everyday life.

When you cut open a pear, and leave the pear uneaten for too long, the inner part of the fruit slowly turns brown. This is because of oxidation. Similarly, the rust that develops on your iron tools or iron fence is caused by oxidation.

Early Pennies

Pennies were not adopted in the United States until the early twentieth century. Before using pennies, individuals used Indian Head cents. However, the penny was adopted in 1909 and replaced Indian Head coins.

The original design of the coin had a Lincoln head on the front of the coin, and a back that had a picture of wheat stalks. In 1959, this design was changed. Now, the back of the penny has a picture of the Lincoln Memorial.

What Are Pennies Made Of?

Before World War Two, pennies in the United States were composed almost entirely of copper. Specifically, the penny was made of about ninety five percent copper, and a five percent combination of tin and zinc.

However, during World War Two, the government needed the copper that was used to create pennies. Thus, at the end of 1942, Congress passed an act that changed the composition of the coins. The new coins were composed of low grade carbon steel and zinc.

The composition of the coins returned to copper shortly after the war was over. Then, in 1962, the Congress passed another act that decreed for pennies to be created from ninety five percent copper and five percent zinc.

When the price of copper rose dramatically in the mid eighties, Congress again had to change the composition of the penny. The penny is now composed almost entirely of zinc (more than ninety seven percent), and less than three percent copper.

The base of the coin is zinc, and there is a thin layer of copper that covers the coin. This composition of the penny has not been altered since 1982. The last copper coin was manufactured on October 22, 1982.

Oxidation Process

Since pennies are composed of a copper alloy, the oxidation process results in a change of color over time. Pennies do not rust, but rather their exterior color alters. When the copper is oxidized, the color changes to a green color and also forms a patina.

Patina coats the penny. It is a combination of different compounds, and the patina that results from oxidation actually protects the penny from rusting. This result from oxidation is unique to the metal copper, and other metals do not have this reaction during oxidation.

When a penny becomes oxidized, it attracts minerals from its external environment. For example, this means that it attracts minerals from the dirt, dust, or even the individuals that are handling the money. Thus, although the oxidation should turn the pennies green, due to this process, the pennies become brown over time.