The origin of Glass- Why they are transparent?

Archaeological findings suggest that glass was first created during the Bronze Age in the Middle East. To the southeast, in Egypt, glass beads have seen found dating back to about 2500 B.C.E. Glass is made from a mixture of silica sand, calcium oxide, soda, and magnesium, which is melted in a furnace at 2,730°F (1,500°C). Most early furnaces produced insufficient heat to melt the glass properly, so glass was a luxury item that few people could afford. This situation changed in the first century B.C.E. when the blowpipe was discovered. Glass manufacturing spread throughout the Roman Empire in such quantities that glass was no longer a luxury. It flourished in Venice in the fifteenth century, where soda lime glass, known as ‘cristallo’, was developed. Venetian glass objects were said to be the most delicate and graceful in the world.

How glass was made?

It all begins in the earth’s crust, where the two most common elements are silicon and oxygen. These react together to form silicon dioxide, whose molecules arrange themselves into a regular crystalline form known as quartz. Quartz is commonly found in sand, where it often makes up most of the grains and is the main ingredient in most types of glass. You probably noticed that glass isn’t made of multiple tiny bits of quartz and for good reason. The edges of the rigidly formed grains and smaller defects within the crystal structure reflect and disperse light that hits them. But when the quartz is heated high enough, the extra energy makes the molecules vibrate until they break the bonds holding them together and become a flowing liquid, the same way that ice melts into water. Unlike water, though, liquid silicon dioxide does not reform into a crystal solid when it cools. Instead, as the molecules lose energy, they are less and less able to move into an ordered position, and the result is what is called an amorphous solid. A solid material with the chaotic structure of a liquid, which allows the molecules to freely fill in any gaps, this makes the surface of lass uniform on a microscopic level, allowing light to strike it without being scattered in different directions.

How glass is transparent?

Ancient glass materials found in Rome.

Why light is able to pass through glass rather than being absorbed as with most solids? You may know that an atom consists of a nucleus with electrons orbiting around it, but you may not know that an atom has a lot of empty space. So, light passes through these atoms easily without hitting any of these particles. Then why aren’t all materials transparent? This is because, the different energy levels those electrons in an atom can have. Consider an atom of an iron, an electron in it initially assigned to move in a certain orbit. But if it had the enough energy; it could reach the exited state and jump to a closer orbit. So, one of the light photons passing through can provide the needed energy. But there is one thing; the energy from the photon has to be the right amount to get an electron to the next orbit. Otherwise, it will just let the photon pass by, and it just so happens that in glass, the electrons are placed so far from each other, that the photons of visible light can’t provide enough energy for an electron. Photons from ultra violet light give just the right amount of energy, and are absorbed. That’s why you can’t get a suntan through glass. This amazing property of being both solid and transparent has given glass many uses throughout the centuries.

 In the 1950s Sir Alastair Pilkington introduced ‘float glass production”, a revolutionary method still used to make glass. Other developments have included safety glass, heat resistant glass, and fiber optics, where light pulses are sent along thin fibers of glass. Fiber optic devices are used in telecommunications and in medicine for viewing inaccessible parts of the human body.