What is behind a mirror?

Answered by Douglas Hiatt

When we look at a mirror, we often take for granted what lies behind its reflective surface. However, the composition and construction of mirrors are quite fascinating. Let’s delve into the world behind a mirror and explore what lies beneath.

1. Reflective Layer: The reflective layer is the key component that allows mirrors to reflect light. In traditional mirrors, this layer is typically made of metals like silver, tin, nickel, or chromium. These metals are deposited onto the back surface of the mirror using a wet process. The metal layer is responsible for reflecting most of the light that falls onto the mirror and creating our reflection.

2. Alternative Reflective Materials: While metals are commonly used, alternative materials can also serve as the reflective layer. One such example is aluminum, which can be deposited onto the mirror’s surface through sputtering or evaporation in a vacuum. Aluminum mirrors are often used in applications where high reflectivity is desired, such as telescopes.

3. Multiple Layers: In some cases, mirrors may have multiple layers of transparent materials with suitable indices of refraction. These layers help enhance the mirror’s reflectivity and durability. For instance, a layer of silicon dioxide or titanium dioxide may be added to protect the reflective metal layer from corrosion or oxidation.

4. Glass Substrate: The reflective layer is typically applied onto a glass substrate, which forms the main body of the mirror. The glass used in mirrors is usually high-quality, flat, and free from imperfections. It provides a smooth and stable surface for the deposition of the reflective layer.

5. Backing Paint: To protect the reflective layer from potential damage, a backing paint is applied to the back surface of the mirror. This paint layer also prevents moisture or other contaminants from reaching the reflective layer and causing degradation. The color of the backing paint can vary, but it is commonly black to minimize the visibility of the mirror’s backside.

6. Protective Coatings: In some cases, additional protective coatings may be applied to the mirror’s surface to enhance its longevity. These coatings can improve scratch resistance, reduce glare, or make the mirror easier to clean. For example, a thin layer of silicon dioxide may be added to improve the mirror’s durability and resistance to environmental factors.

7. Framing and Mounting: mirrors are often framed and mounted to make them functional and aesthetically pleasing. Frames can be made of various materials such as wood, metal, or plastic, and they serve to protect the edges of the mirror while also providing support for hanging or mounting.

Understanding the construction of mirrors can give us a greater appreciation for their functionality and the craftsmanship involved in their production. Next time you look into a mirror, take a moment to ponder the intricate layers and materials that come together to create your reflection.