Brief history of glass

　　Man made glass more than 5000 years ago. Archaeological evidence shows that in Egypt and Mesopotamia in 3000 BC, people have made some small handicrafts such as amulets and beads with glass.

　　By around 1500 BC, people’s skills in making glass were becoming more and more mature, and the first glass container appeared in human history. The ancient Egyptians also mastered the technology of coloring glass. They know that adding copper powder to glass can make red glass, adding cobalt powder can make blue glass, and adding tin powder can make white glass … These colored glasses are used by some unscrupulous businessmen to pretend to be jewelry, deceiving many people.

　　In the 1st century BC, Syrians invented the technology of blowing glass. With this technology, making glass becomes simple, fast and cheap. Since then, the glass industry has flourished in the Roman Empire and quickly spread to other countries under the rule of the Roman Empire.

　　Around the 1st century A.D., the Romans discovered that adding a proper amount of manganese dioxide to glass could make colorless glass, so they began to make windows out of glass and install them on buildings. Although the optical performance of glass at that time was very poor, glass windows were still "standard" for buildings in Rome, Pompeii and other places.

　　In the 8th century, Venice concentrated a large number of glass workers and became the glass manufacturing center at that time. Later, with the progress of science and art, people "played" more tricks, such as dyeing paint on glass and drawing colorful patterns. Many churches we see now have stained glass windows, which is the architectural style left over at that time.

　　In the mid-15th century, a glass worker in Venice invented a new type of super transparent glass. Soon, this new type of glass was used to make telescopes, thermometers, flasks, microscopes and other scientific instruments, which led to many important scientific discoveries.

　　Around the 18th century, the glass manufacturing center in Europe moved from Venice to Britain. At that time, the output of British glass factories was very high. At one time, the British government would levy taxes based on the number of windows in each house, on the grounds that wealthy families would install more windows, and of course they should pay more taxes. However, "there are policies above and countermeasures below", and many families simply blocked the windows in order to avoid paying taxes-this story shows that the use of glass was quite common in Britain at that time.

　　Since the industrial revolution, steel and glass have become important building materials for modern architecture. In 1851, Britain built a "Crystal Palace", which only used steel and glass. This miraculous building was also the exhibition hall of the first World Expo in London. In 1950s, a German architect innovatively covered the facade of the building with a layer of glass, which made the appearance of the building look unprecedented. This innovative design can be successful, on the one hand, because there is a reinforced frame inside the modern building, and the facade does not need to bear the weight of the whole building; On the other hand, because the strength of glass has become higher. So many skyscrapers we see now have glass facades.

　　Nowadays, scientists and engineers have developed a variety of glasses, which have important uses in many fields. For example, there is a kind of glass that can quickly transmit network information, that is, optical cable, which is filled with thousands of glasses as thin as hair, in which communication signals shuttle in the form of light and quickly transmit information to all parts of the world.

　　Sand and glass

　　The main component of glass is silica, that is, Shi Ying, which is one of the most common minerals on the earth. The sand that can be seen everywhere is actually a small particle in Shi Ying. When Shi Ying is heated to 1400℃, it will melt, then become soft and become a transparent, viscous liquid-then it will be cooled and shaped, and then the glass will be finished.

　　How did sand become glass?

　　On the atomic scale, silicon dioxide is composed of silicon atoms and oxygen atoms, and they are arranged in order in Shi Ying. For example, a group of silicon atoms and oxygen atoms are neatly arranged to form a "queue" with specific arrangement rules, and the whole "queue" is Shi Ying particles. A structure like this, which consists of a large number of microscopic substance units (such as atoms and ions) arranged in an orderly manner according to certain rules, is called a crystal.

　　After Shi Ying melted, its internal crystal structure was destroyed, or the original "queue" was disrupted, and silicon atoms and oxygen atoms began to "run" freely, making Shi Ying change from solid to liquid. Of course, if the liquid Shi Ying can be cooled quickly, the crystal structure will be re-formed, just like the silicon atoms and oxygen atoms that "run" at will "stand" in the original position in the queue again.

　　However, if the cooling speed is too fast, so that silicon atoms and oxygen atoms can’t return to their original positions, then they can only be condensed in their current positions. Therefore, the final glass is like a snapshot of liquid Shi Ying. Scientists have a special name for this state of solid, called "amorphous solid", which means that this kind of solid is different from crystal, and there is no orderly arrangement rule in its internal structure.

　　Why is glass transparent?

　　We can’t go straight through the glass, but our eyes can see the objects on the other side through the glass. Why?

　　We can see an object because the light is reflected or scattered after it reaches this object, which makes some light enter our eyes and let us see the shape and color of the object. Only a part of light energy is received by our eyes, and the rest is absorbed or intercepted by objects.

　　How much light an object can intercept depends on the kind of molecules or atoms that make it up.

　　Most of the atoms in the glass don’t intercept light, and almost all the light that reaches the glass can be received by the eyes (glass can intercept ultraviolet light, but our eyes can’t see ultraviolet light). In addition, glass is not crystal, and there is no edge edge edge of crystal structure inside, so it will not scatter light. So, when the light reaches the glass, it will go straight through without changing its direction.

　　However, if a piece of glass is slightly thicker in some places, the propagation path of light will be bent, which is the working principle of a prism.

This article is from Science Illustrated.