How Glass is Made
Glass is an amorphous non-crystalline solid that has numerous applications in our modern world. Its optical and physical properties make it suitable for innumerable applications such as:
- flat glass that are used in mirrors and windows;
- container glass like those used for bowls and drinking glasses;
- optics such as those used in microscope and telescope;
- optoelectronics material used for optical fiber and photoresistors;
- laboratory equipment such as flasks and test tubes;
- thermal insulators such as glass wool; and
- reinforcement fiber such as glass-reinforced plastic and fiber reinforced concrete.
What is glass?
Glass is a combination of silica (SiO2) and other minerals that are melted together at extremely high temperatures. The most common form of silica is sand. It also occurs naturally in a crystalline form called quartz.
The other minerals and ingredients added to silica make it easier to melt and easier to shape once it is melted. Two of the common minerals added to silica are soda ash (NaO2) and lime (CaO). Glass made out of these ingredients is called soda lime glass.
Through the years, other mineral oxides have been added to silica to produce chemically durable and more heat- and shock-resistant types of glass. These include borosilicate, which contains boron oxide (B2O3), and aluminosilicate glass, which contains alumina (Al2O3).
What is the process of making glass?
Glass is made by melting minerals together in extremely high temperature. Silica is combined with other minerals, such as soda ash and lime, and melted in a furnace at temperatures reaching 1700ºC. When these minerals have melted, it becomes a syrupy mass. It is this property of glass that allows it to be poured, blown, pressed, and molded into a variety of shapes and sizes. Glass hardens at room temperature and changes into a form that we are so familiar with.
How is glass formed?
Glass can be formed through three different methods, namely:
- Glass Blowing
- Pressing Method
- Drawing Method
Blowing is the oldest method of forming glass, dating back as far as thousands of years. This method involves dipping one end of a hollow iron pipe into a pot of molten glass. The glass is gathered at the end of the pipe by rotating it. The gathered glass is left to cool at 1000ºC before it’ s rolled on an iron slab to form a parison. It is then reheated and mounted at the end of the hollow iron pipe where a worker gently blows through the pipe to shape it and thin it to the blower’s specifications. When the glass resembles the shape of the final article, it is placed in an iron mold which is always kept wet. The glass is then blown into its final shape forming the interior of the mold.
This process involves placing a hot ball of glass into a mold and pressing it to fill the mold. Most domestic glassware, ashtrays, and other glass containers are made using this method.
This method is used for shaping flat glass to be used for mirrors and windows, or tubes used for TV tubes, florescent lights, and laboratory equipment. Flat glass is made by drawing the melted glass into a tank of melted tin. The tin’s smooth surface forms a flat layer of glass as the molten glass floats on top of it. Glass tubing, on the other hand, is formed by drawing a stream of molten glass around the inside of a cylinder. The cylinder is rotated while a continuous stream of air is blown into the tube to form a continuous glass tube.
