The Glass-Making Process

According to Wikipedia, glass in the common sense refers to a hard, brittle, transparent solid, such as used for windows, many bottles, or eyewear, including soda-lime glass, acrylic glass, sugar glass, isinglass (Muscovy-glass), or aluminium oxynitride. One type of glass which is now widely used either for household appliances or laboratory equipments is soda-lime glass.

The process of making soda-lime glass is quite simple. First, the raw materials such as sand, soda, and limestone, are reduced to powder, which is done in mortars or by horse mills. Sand contains silica (SiO₂), which acts as the main ingredients for making glass. Silica has a very high melting point of over 2300 °C, so in order to lower the melting point and produce glass with better chemical durability, soda (common word for sodium carbonate) and lime (calcium oxide, generally obtained from limestone) are added. Those raw materials are then mixed and transported to furnace, where they are kept in a moderate heat (±1500 °C) for approximately 5 or 6 hours, being frequently stirred about during the process. After melting, homogenization and refining (removal of bubbles), the glass is formed. At this point, plate glass and container glass can be produced by two kinds of process. Plate glass for windows and similar applications is formed by putting the molten glass through rollers, making it perfectly flat, while container glass for common bottles and jars is formed by blowing and pressing methods. In making bottle glass, for instance, removable mould is used so that the bottle glass could stay in shape after the molten glass is being cooled down.