Glass is a versatile substance that has been used by humans since 12,000 BC. It is a supercooled liquid that can be made from natural sources like silicate-rich rocks or by man using silica, soda, and lime. Glass is a rigid liquid that retains liquid properties while behaving like a solid. It is preferred for its resistance to chemical interactions, recyclability, and ability to withstand extreme temperatures.
Glass is an amorphous solid that has existed in various forms for thousands of years and has been produced for human use since 12,000 BC. Its status as a liquid, versus a solid, has been hotly debated. The short story is that glass is a supercooled liquid, which means it’s stiff and static but doesn’t change molecularly between melting and solidifying into the desired shape. It is one of the most versatile substances on Earth, used in many applications and in a wide variety of forms, from clear to tempered and colored varieties, and so on.
Natural glass is created when silicate-rich rocks melt at high temperatures and cool before they can form a crystalline structure. Obsidian or volcanic glass is a well-known example of natural types, although it can also be formed by lightning striking a beach, which contains silicate-rich sand. Early forms were likely filled with impurities and prone to cracking and other instabilities, but examples of beads, vessels, and food materials first appeared in ancient Egyptian culture.
When made by man, glass is a mixture of silica, soda and lime. Sometimes other materials are added to the mix to “freeze” or cloud the glass or to add color. The elements are heated to 1800° Fahrenheit (982° Celsius). The resulting molten liquid can be poured into molds or blown into various shapes, and once cooled, glass is a strong, minimally conductive substance that does not interact with the materials stored within. As a result, it is often used in scientific laboratories to minimize unintentional chemical reactions and to insulate power lines.
Silica is found in a wide variety of natural sources, including, most commonly, sand. Sodium carbonate, or soda, is used to lower the melting point of silica, making the glass light and workable. Soda is called flux, because it lowers the melting point of the mixture. Lime is ground from limestone and makes the mix more viscous, as well as making it less susceptible to the erosive qualities of water and acids.
Glass is a strange substance, which defies easy scientific categorization. It is not a solid, not a gas or even a liquid. Generally, it is classified as a rigid liquid, retaining liquid properties while behaving like a solid. The heat can return it to a viable, liquid form, making it easy to reuse and recycle.
There are many reasons why glass is a preferred material. It resists chemical interactions, is easy to recycle, doesn’t leach chemicals like plastics, and can withstand extreme temperatures, though not at the same time. Tempered or safety glass is used in a wide variety of applications, and virtually all consumers use many forms on a daily basis.
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