Exploring the World of Glass: Ancient and Modern Uses of a Unique Material

Category Technology

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Glass is an ancient material that has been used for a multitude of purposes for centuries. It is both a solid and a liquid and has been essential to the technological revolution of the 20th and 21st centuries. Its unique properties make it ideal for a wide range of applications, from decorative art to solar energy generation.

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Glass is a material of many faces: It is both ancient and modern, strong yet delicate, and able to adopt almost any shape or color. These properties of glass are why people use it to make everything from smartphone screens and fiber-optic cables to vials that hold vaccines.

Humankind has been using glass in some fashion for millennia, and researchers are still finding new uses for it today. It’s not uncommon to hear the oft-repeated factoid that glass is actually a liquid, not a solid. But the reality is much more interesting – glass does not fit neatly into either of those categories and is in many ways a state of matter all its own. As two materials scientists who study glass, we are constantly trying to improve our understanding of this unique material and discover new ways to use glass in the future.

Glass was one of the first materials used by humans for decoration, with the earliest known glass beads dating back to about 5000BCE.

What is glass? .

The best way to understand glass is to understand how it is made.

The first step to make glass requires heating up a mixture of minerals – often soda ash, limestone and quartz sand – until they melt into a liquid at around 2,700 degrees Fahrenheit (1,480 Celsius). In this state, the minerals are freely flowing in the liquid and move in a disordered way. If this liquid cools down fast enough, instead of solidifying into an organized, crystalline structure like most solids, the mixture solidifies while maintaining the disordered structure. It is the atomically disordered structure that defines glass.

The Romans are credited with developing glass-blowing techniques, which vastly increased the range of shapes and sizes that could be made.

On short timescales, glass behaves much like a solid. But the liquidlike structure of glass means that over a long enough period of time, glass undergoes a process called relaxation. Relaxation is a continuous but extremely slow process where the atoms in a piece of glass will slowly rearrange themselves into a more stable structure. Over 1 billion years, a typical piece of glass will change shape by less than 1 nanometer – about 1/70,000 the diameter of human hair. Due to the slow rate of change, the myth that old windows are thicker at the bottom due to centuries of gravity pulling on the slowly flowing glass is not true.

The invention of lead crystal in the late 1700s greatly improved the clarity and beauty of glass products.

Colloquially, the word glass often refers to a hard, brittle, transparent substance made of fused sand, soda and lime. Yet there are many types of glass that are not transparent, and glass can be made from any combination of elements as long as the liquid mixture can be cooled fast enough to avoid crystallization.

From the Stone Age to today .

Humans have been using glass for more than 4,000 years, with some of the earliest uses being for decorative glass beads and arrowheads. Archaeologists have also discovered evidence of 2,000-year-old glass workshops. One such ancient workshop was uncovered near Haifa in modern Israel and dates back to around 350 C.E. There, archaeologists discovered pieces of raw glass, glass-melting furnaces, utilitarian glass vessels and debris from glass-blowing.

Today, glass is one of the most recycled materials, with up to 95% of all glass bottles being recovered in some countries.

Modern glass manufacturing began in the early 20th century with the development of mass production techniques for glass bottles and flat glass sheets. Glass became an essential part of the electronics and telecommunications industry in the latter part of the 20th century and now forms the bacis of smartphone screens, LEDs, televisions and fiber optics. Advances in manufacturing have also led to glass bottles becoming lighter and stronger and to the production of exotic types of glass – such as opaque glass – for an array of different uses.

The thickness of old windows does not change because the glass needs very long periods of time – up to a billion years! – to undergo any sort of change.

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