Why Glass Is Transparent? (Surprising Answer!)

Glass is such a commonly used material in our everyday lives that we literally see right through it without a second thought. It’s in our screens, windows, watches, mirrors, and appliances that we use all the time, and that’s just to name a few. But did you ever wonder how glass is made or what it’s made from?


In this article, we’ll briefly explain the nature of glass and why glass is transparent, despite being made of proper solid and visible materials.

What Is Glass?

Glass is a brittle, non-crystalline material and an inorganic solid that is known for its transparent appearance. There are four main types of glass: 

  • Annealed glass
  • Toughened glass 
  • Heat-strengthened glass
  • Laminated glass

To understand why glass is transparent, we have to know how it is made. Let’s examine this.

How Is Glass Made?

In glass plants, ordinary sand is mixed with glass waste from recycling, limestone, and soda ash, and heated to roughly ​​3090 degrees Fahrenheit. 

The soda is added to reduce the sand’s melting point and help save energy, but it causes the produced glass to dissolve in water. This is why the limestone is added to prevent this from happening.

Once the sand has melted, it is made into flat sheets of glass used for windows or poured into different molds to make glasses, bottles, and all kinds of shapes of glass products.

Glass manufacturers use slightly different variations of this process depending on the type of glass they produce, like toughened, bullet-proof or color-tinted glass.

Is Glass Solid or Liquid?

This is a very common and interesting question. The answer to this question, however, isn’t very straightforward. Glass is both solid and liquid, but it’s also neither. It’s something that we refer to as an amorphous solid.

An amorphous solid is a solid that is different in its crystalline structure from other solids, like metal, for example. The molecules of glass arrange themselves in an irregular pattern, making them different from most solids, but also unlike liquids. Glass is described as a supercooled frozen liquid.

In other words, glass could be described as having some characteristics of both solids and liquids. Its internal structure resembles solid in its order and liquid in its randomness.

It’s also worth noting that glass isn’t the only amorphous solid. There’s a type of water called amorphous ice, which looks like regular ice but behaves more like water. There’s also amorphous silicon, which is used to manufacture solar cells.

Why Is Glass Transparent?

We’ve become so used to the fact that glass is a transparent solid material that we can see through and we rarely think about it anymore. However, there’s a scientific explanation to how this is possible.

Glass is made of SiO2 (silicon dioxide) which has a weak attraction force. This causes particles like air molecules to come together, allowing light rays to travel through it in a straight line with ease and without changing direction.

Glass isn’t actually made of a single piece of glass, but of many very thin triangular and square-shaped pieces that are stuck together called “an array”. Since light refracts or bends when it hits an object according to its shape, this decides how much light reaches your eyes.

As light rays follow the edges of these shapes and match their angles, they end up traveling through glass easily and without bending much, making the glass appear transparent.

Why Is Glass Transparent While Sand Isn’t?

We’ve explained earlier how glass is mainly made of sand, so how can glass be transparent while sand itself is yellow and opaque?

While glass allows light to pass through easily, causing it to be transparent, the sand itself doesn’t allow much light to travel through it well. Since there are many air pockets and spaces between the sand grains, sand reflects most of the light that falls on its surface, causing it to appear opaque.

Is Glass Transparent to Ultraviolet and Infrared Too?

While glass is transparent to visible light, it’s opaque to infrared and ultraviolet rays. These are wavelengths that aren’t visible to the human eye, so they easily pass through glass.

Visible light has a wavelength between 380 and 700 nanometers. These lights pass through the glass easily, as the light rays don’t interact with glass atoms.

Ultraviolet radiation, which has a shorter wavelength than visible light, gets absorbed by the glass, so it doesn’t reach our human eyes.

Infrared radiation has a longer wavelength than visible light. The glass partially reflects and absorbs most of the radiation back, allowing just a small amount of the radiation to pass through.

Why Do Glass Cracks Look Opaque?

If you’ve ever broken any glass, either on a window, smartphone screen, or any glass object, then you must have noticed that the cracked edges appear dark greenish or opaque. Why are cracks not transparent like an intact glass object is?

When a glass is broken, cracks expose the rough edges. When a light ray hits these rough edges, it’s split into multiple rays and is reflected away in different directions. This doesn’t allow for a proper reflection image to form.

Another reason is that when a light ray enters a glass through a cracked edge, some of the light gets trapped inside and doesn’t reflect outwards due to internal reflections.

Bottom Line

Glass is transparent simply because it allows all light that falls on it to pass through easily. This happens because glass has a weak attractive force and is a great medium for light to travel. This is in contrast to, for example, water, which reflects most of the light that hits its surface due to its strong attractive force.

In other words, the molecules in glass are composed in a way that their electrons barely interact with photons of light passing through. To human eyes, this makes a material look transparent.