How glass is made

It’s usually encountered as a transparent pane, so it is easy to look past – or right through – glass. But have you ever stopped to think not about the view beyond your window, but of the window itself? This impressively clear, firm material before you is just one of many variations of glass. Glass can be transparent or opaque, coloured or clear, bullet-stoppingly thick or wafer thin. Every day we use it, whether we drink from a bottle made out of it, decorate our homes with it or tap the touchscreens on our mobile phones and tablets. Glass is everywhere. It can be dangerous. When broken it can form shards that can inflict nasty injuries, while in its ornamental form it’s so delicate that an accident can mean a priceless artefact is shattered into thousands of pieces. Either way, glass is usually approached with an element of caution. But how did it come to hold these properties?

Before being manipulated, the components of this handy material are nothing but a pile of sand, rock and minerals. An unlikely combination of naturally occurring ingredients, when exposed to extreme heat they produce a fascinating reaction. Molten glass is the product’s middle stage, between sand grains and window panes. Baking in a fiery furnace, the red-hot liquid is unrecognisable compared to its final state. 

At an atomic level, glass behaves in surprising ways at room temperature. Although it feels solid and is a hard substance to touch, scientists have discovered that glass never reaches a fully solid stage. The reason glass appears to be neither fully liquid nor solid is because it is structured more like a gel. When glass cools from being a searing, orange inferno, rather than crystallising and its atoms forming a lattice structure, it takes on a more random arrangement instead, creating a tight jam of particles. This makes the glass sturdy enough to appear solid without carrying all the properties of a solid.

As it is, glass is light, transparent and ideal for masses of applications. However, once turned from solid sand and rock to glass, it can’t be converted back. This makes glass difficult to recycle. To reuse glass, it can be melted back into its molten form, added to a new batch and reshaped for a different glass product. Recycling glass is vital to limit the natural resources humans use over time. If everybody put their glass bottles into the recycling bin, the glass already in circulation could be continuously reused without the need to make more. Theoretically this would mean having an eternal supply of glass, without having to use more of Earth’s raw materials.

Over 5,000 years have passed since people first explored a new substance that we now know as glass. The 21st century hasn’t failed to bring new uses for this flexible and widespread resource. New inventions bring new physical needs, while our expanding knowledge of science only widens the possibilities for a simple and ancient base material. As we evolve to develop technology further, who knows what is possible in the future of glass?