Many smooth surfaces show images of the objects near them. The surfaces that show the most lifelike images are called mirrors. The earliest mirrors were simply pieces of polished metal. Mirrors today are most often flat sheets of glass with a coating of metal on the back.

Reflection

The appearance of an image in a mirror is called reflection. Reflection happens when light hits a surface. If the light cannot pass through the surface, it bounces off, or reflects. Most surfaces—including your body—absorb some light and reflect some light. Mirrors, however, reflect almost all the light that hits them. The metallic coating on the back causes the reflection.

When you stand in front of a mirror, your body reflects patterns of light that hit the mirror. Those patterns of light bounce off the mirror and go right back to your eyes. Your brain then interprets the patterns of light as an image of yourself in the mirror.

Types of mirrors

Most mirrors, called plane mirrors, are flat. Images in a plane mirror are reversed. For example, if you raise your right hand while looking in a mirror, you will appear to raise your left hand. People use plane mirrors to check their appearance. They also hang them as decorations in homes and public places.

Curved mirrors can distort images, or change their shape and size. They can also reverse images and flip them upside down. Convex mirrors curve outward, like a dome. They make objects appear reversed and smaller than their actual size. Side mirrors on cars are convex. Concave mirrors curve inward, like a bowl. At a distance, they make objects appear upside down. Objects close to a concave mirror, however, appear right side up and larger than their actual size. Makeup and shaving mirrors are often concave. Other types of curved mirrors are used in telescopes and with lasers.

How mirrors are made

Mirrors are made in factories with special machinery. First, sheets of glass are polished smooth, cut to the correct size, and cleaned. Next, the back of the glass is covered with a thin layer of metal. A liquid solution of metal may be poured onto the surface, or a machine may use electricity to coat the glass with a metallic film. Finally, the metal is covered with copper, varnish, or paint to protect it from scratches.

Silver and aluminum are two of the most common metallic coatings. Mirrors can also be made with other metals, including gold, tin, and lead. Rearview mirrors in cars often have a lead coating. Lead does not reflect as much as other metals. This prevents drivers from being blinded when headlights from behind shine on the mirrors at night.