Glass occurs naturally and can also be created through a man-made processes. All of the glass we see around us is created synthetically and is made with a different chemical recipe depending on what properties we want it to have.
Batch - a combination of sand, sodium carbonate and calcium carbonate.
Glass is primarily made from silica, which is found naturally in sand. We also add soda ash (Sodium Carbonate) and limestone (Calcium Carbonate) to help lower the melting point of the silica. Depending on what the use of the glass will be, other ingredients might be added, such as: lead, boron, and chemicals that add colors. These raw materials are called “batch.”
Batch is then put into a hot furnace, where it takes many hours for it to melt down and mix together for the different chemicals to form into a smooth liquid. The heat required to melt the batch into liquid glass is enormous and the generation of all that heat energy results in the release of CO
2 into the atmosphere.
Batch is melted down at temperatures hotter than molten lava.
The liquid glass is now hotter than molten lava and takes a long time to cool. To make glass for windows, it needs to be made flat. To make sure that the glass is completely flat, we can pour the glass on a river of molten Tin. Tin is a metal that has a lower melting point than glass, so the glass can be poured out onto the tin and cools as it floats down the river. This is called Float Glass.
Liquid glass is poured out onto a river of liquid Tin.
The tin river can vary in length, but can be made to be extremely long to allow the glass time to cool evenly. In the image below, we see a cooling tunnel over a 1/4 mile long.
The Tin river inside this structure stretches for over 1/4 mile!
Finally, glass comes out in one long sheet and is further cooled for cutting.
Glass comes out in one long sheet so it can cool before it's cut and shipped out of the factory.
Glass recycles better than most other things that are recycled. There is no loss of material when recycling glass, but recycled glass will keep its color. Most of the time, glass will be separated into different colors of glass before they’re crushed down. Every metric ton (1,000 kg) of waste glass recycled saves 315 kilograms (694 lb) of carbon dioxide from being released into the atmosphere that would be released when making new glass.
Crushed glass ready for recycling.
"Glass recycling information sheet". Wasteonline.org.uk Retrieved 22 April 2018.
"Glass, Common Wastes & Materials". US EPA. Retrieved 22 April 2018.