Glass: A Versatile Material

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On 18th May 2021, the UN General Council approved a joint application by the International Commission on Glass (ICG), the Community of Glass Associations (CGA) and ICOM-Glass that 2022 be declared a United Nations International Year of Glass. This year celebrates and underlines the scientific, economic and cultural roles of glass. Glass supports many vital technologies, facilitates sustainability and a green world and enriches our lives, yet often goes unnoticed. 

A timeline of how glass-making has developed

History of Glass

Glass was first made in the ancient world, but little is known about man’s first efforts to make glass. The earliest known man-made glass dates back to around 3500BC, with finds in Egypt and Eastern Mesopotamia. Discovery of glassblowing around the 1st century BC was a major breakthrough in glassmaking. There were amulets and solid beads which were made in Mesopotamia as far back as 2500BC. Glass-making was further developed in Egypt around 1500BC. 

While glass was mainly valued for its colour and ornamental use, a turning point was formed in the 1st century BC, when glassblowing was invented. With the establishment of the Roman Empire, this new technology was adopted and spread quickly. The Romans also made the first glass windows; people could now look through glass instead of just looking at it. Glass began to undergo industrialization and spread to other parts of the world.

Besides being used as windows, the magnification properties of glass was discovered as well, leading to the invention of eyeglasses in the 13th century. The technology of glass lenses eventually led to the invention of microscopes and telescopes. This opened possibilities like the study of microorganisms and astronomy in the 17th century.

The development of clear glass also led to equipment that we use in modern chemistry and medicine today. This is largely due to its inert properties, allowing scientists to measure, mix and put chemicals and materials under different pressures.

The Glass Manufacturing Process

To produce glass, sand is mixed with lime and soda ash before heated at extremely high temperatures. Once the sand is melted, it is poured into moulds to make bottles, glasses, and other containers, or ‘floated’ (poured on top of a big vat of molten tin metal) to make perfectly flat sheets of glass for windows. 

Unusual glass containers are still sometimes made by ‘blowing’ them. A “gob” (lump) of molten glass is wrapped around an open pipe, which is slowly rotated. Air is blown through the pipe’s open end, causing the glass to blow up like a balloon. With skillful blowing and turning, all kinds of amazing shapes can be made.

Glass makers use a slightly different process depending on the type of glass they want to make. Usually, other chemicals are added to change the appearance or properties of the finished glass. For example, iron and chromium-based chemicals are added to the molten sand to make green-tinted glass. Oven-proof borosilicate glass (widely sold under the trademark PYREX®) is made by adding boron oxide to the molten mixture. Adding lead oxide makes a fine crystal glass that can be cut more easily. Highly prized cut lead crystal sparkles with colour as it refracts (bends) the light passing through it. 

Some special types of glass are made by a different manufacturing process. Bulletproof glass is made from a ‘sandwich’ or laminate of multiple layers of glass and plastic bonded together. Toughened glass used in car windshields is made by cooling molten glass very quickly to make it much harder. Stained (coloured) glass is made by adding metallic compounds to glass while it is molten. Different metals give the separate segments of glass their different colours.

Natural Forms of Glass

The very first glass known was obsidian, a black volcanic glass used for making weapons and decorative objects. Obsidian can form when hot lava cools quickly after being expelled from a volcano. Obsidian is commonly found within the margins of lava flows known as obsidian flows, where the high silica content induces a high viscosity and polymerization degree of the lava. Obsidian is mineral-like, but not a true mineral because, as a glass, it is not crystalline. Its composition is too complex to comprise a single mineral. It is sometimes classified as a mineraloid. Though obsidian is usually dark in colour similar to mafic rocks such as basalt, obsidian’s composition is extremely felsic. Obsidian consists mainly of silicon dioxide, usually 70% or more. Crystalline rocks with obsidian’s composition include granite and rhyolite.

Glass can also be formed by lightning. When lightning strikes sand which is high in silica or quartz, the heat fuses the sand particles together into a tube of glass. This forms a ‘fulgurite’. Usually fulgurites are long, hollow tubes of sand grains. Fulgurites can stay hidden in the sand for decades and is easily broken.

Environmental Impacts of Glass Manufacturing

The production and use of glass have a number of environmental impacts. New glass is made from four main ingredients: sand, soda ash, limestone and other additives for colour or special treatments. Although there is no shortage of these raw materials as yet, they all have to be quarried, using up natural resources and energy for extraction and processing.

Glass is fully recyclable and can be endlessly recycled with no loss of quality. Domestic waste glass, which is also known as cullet, is easy to recycle. The United Kingdom currently recycles around 71% of container glass such as bottles and jars. In contrast, Singapore only recycles approximately 20% of its glass waste.

By simply recycling our glass, we can reduce non-renewable fossil fuel usage and emissions of carbon dioxide.

How to Recycle Glass

Glass bottles such as wine bottles, beer bottles, condiment bottles and even skincare product bottles and jars can go into the blue recycling bin or chute; remember to empty and rinse them first before disposing them. To prevent glass breakage, bag the glass bottles with other recyclables to cushion the landing when the glass items are placed in the recycling chute. This way, any breakage stays within the bag. Broken glass can still be collected by recyclers and processed into new bottles again!

Written by Norain Binte Hassein, HOD Science, West Spring Primary School
Illustrations by Sung Jernin


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