A mirror is an object that reflects an image. Mirrors are typically made by applying a reflective coating to a surface. The most common material used for producing mirrors is glass due to its smooth and rigid surface which can be given a highly reflective finish. So in short, a mirror contains glass but it has a reflective coating on it that differentiates it from regular glass. Let’s take a deeper look at mirrors and glass to fully understand their relationship.
What is Glass?
Glass is a hard, brittle and transparent material made by melting together sand with soda, lime and other ingredients and then cooling the mixture quickly. The main ingredient of glass is silicon dioxide or silica sand. Glass is non-crystalline, which means its molecules do not arrange themselves in a regular repeating pattern.
Glass can be made into various shapes while molten by processes like blowing, pressing, casting or spinning. It is used widely in windows, tableware, decorative art objects and lenses. Other common uses include glass bottles, jars, light bulbs, cathode ray tubes and flat panel displays.
The most familiar type of glass is soda-lime glass made of about 70% silica sand along with soda, lime, potash and other ingredients. Borosilicate glass contains boron trioxide which makes it resistant to thermal shock. Aluminosilicate glass is more shock and heat resistant. Lead oxide can be added to produce lead glass known for its clarity and brilliance.
What is a Mirror?
A mirror is simply a reflective surface that forms an image by bouncing light off of it. Mirrors are commonly made by coating a piece of glass with a metal like silver, though metals like copper or aluminum can also be used. The coating is applied to the back of the glass and protects it from corrosion while providing the reflective surface.
When light hits the mirror, some of it goes through the glass while some is reflected by the metal coating on the back. We see an image in the mirror because the reflected light bounces off the metal layer and returns through the glass into our eyes. So mirrors have the same base material (glass) but are differentiated by the reflective coating.
Mirrors can be designed for visible light wavelengths only or for a broader spectrum including ultraviolet or infrared. They are used widely to reflect images and for scientific work including lasers, telescopes, microscopes and industrial machinery.
Manufacturing Process of Mirrors
Here are the basic steps to make a common household mirror:
- Start with a piece of float glass which is an extremely flat sheet of glass made by floating molten glass on a bed of molten metal.
- Clean the surface of the glass thoroughly to prepare it for coating.
- Apply a coating of silver in a vacuum chamber. Modern mirrors use aluminum or other metal coatings too.
- Seal the silver coating with copper and then paint the back of the mirror to fully protect the reflective layer.
- Inspect the mirror for defects in reflection and discard any pieces with flaws.
- Cut the finished mirrors to the desired shapes and sizes.
So the base material of a mirror is glass. But it goes through specialized manufacturing processes like adding a metal coating and protective backing to turn it into a reflective surface.
Similarities Between Glass and Mirrors
Despite their differences, glass and mirrors share some key similarities since mirrors are derived from glass:
- They both have glass as the foundational component.
- The glass surface needs to be flawless and smooth.
- High purity glass is required for clarity.
- They are brittle and prone to cracking or breaking.
- Can be molded into various shapes and sizes.
- They transmit light clearly, except where mirrors have reflective coating.
- Are used extensively in architecture for windows, doors, facades, etc.
Key Differences Between Glass and Mirrors
| Glass | Mirror |
|---|---|
| Transparent to allow light to pass through. | Reflective surface bounces light. |
| Main ingredient is silica or sand. | Has a metallic coating on the back side. |
| Used for transparent applications. | Used for reflection of images. |
| Does not form images. | Forms clear images by reflection. |
| Surface needs to be smooth but not perfectly flat. | Extremely stringent flatness and smoothness requirements. |
| Molded into end products like bottles, glasses, etc. | Often cut, beveled or drilled before use. |
Conclusion
While glass and mirrors have some similar characteristics, mirrors have additional coatings and go through specialized manufacturing processes to make them reflective. The base material of mirrors is glass. But the key difference lies in the thin layer of metal like silver or aluminum applied to the back of the glass. This coating bounces light to create clear reflections on the other side. Without the reflective backing, a mirror would simply act like ordinary transparent glass.
So in summary, while mirrors contain glass and share many of its attributes, the mirrored surface makes them a distinct type of glass engineered specifically for reflection. Calling a mirror just glass fails to account for the critically important metal coatings and treatments that differentiate mirrors from regular glass.
