How Glass is Made

stacks of empty bottles

Sand, soda ash, and limestone are combined to make glass.

Glass is made from sand, soda ash, and limestone. Sand is the main ingredient in all types of glasses, but the type of sand used depends on the quality of glass being made. Soda ash is used to remove impurities from the sand and limestone makes it harder or tougher to break. Other ingredients are also added depending on what type of glass is being made – for example, some types require iron oxide to give them color; other types may include lead oxide or calcium oxide for additional strength or clarity.

Glass is made in two steps — melting and forming.

The first step involves melting the ingredients together, which are sand (silica), soda ash (sodium carbonate), limestone and sodium bicarbonate.

The molten glass mixture is usually contained in a furnace called a tank melter. The second step involves shaping the glass into different shapes by blowing air through an extrusion pipe that pushes out the molten material into molds containing water, which cools and hardens it as it’s being shaped.

The first step in making glass is to mix the ingredients — sand, soda ash, and limestone — until they are the same size grains.

The first step in making glass is to mix the ingredients—sand, soda ash, and limestone—until they are the same size grains. Like flour and water, this makes a very thick sludge that can be poured into a mold. 

In the melting phase of glass making, the mixture goes into a furnace and becomes molten at 2,550 degrees Fahrenheit.

The melting phase is the easiest part of glass making, since it necessitates nothing but heating a tank full of molten glass to 2,550 degrees Fahrenheit (I know, that doesn’t sound very easy relatively). To do this, you heat up your furnace to 1,600 degrees Fahrenheit and then turn off all your ovens. Then you turn on an electric heater connected to a thermostat that heats up only when necessary: at exactly 2:30 pm every day (or whenever it gets dark outside). The temperature in the furnace rises until it reaches 2,550 degrees Fahrenheit—and then stays there until the next morning at 6 am. At this point all that’s left is letting go of the glass mixture so it can cool into sheets or rods or other shapes before being shipped off for use in things like windows and mirrors.

Man pouring a pot of golden liquid glass into a black shaping mold.
Man pouring liquid glass

While in its molten state, the glass is transformed into different shapes.

After being melted and cooled, glass is ready for shaping. Glass can be shaped into many different forms: rods, tubes, sheets, mosaics and more. The type of glass that is used determines what type of shape the glass will take on when it’s heated. 

The furnace where the process starts is called a tank melter.

The tank melter is the furnace where the process starts. It’s made of steel and usually rectangular or cylindrical in shape, between eight and twelve feet long and four to six feet wide. Tank melters are designed to contain a batch size between twenty-five and thirty tons of glass, which takes about four hours to melt down (and then another two and a half hours for it reach its full temperature). This is because glass actually has a relatively low specific heat.

From there, the formed glass goes on an annealer conveyor where it cools down over a period of 12 to 24 hours so that it doesn’t break during that process.

The glass is cooled slowly so that it doesn’t crack, break, or shatter in this process. It’s also cooled slowly so that it doesn’t fracture.

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