How Modern Glass is Made

A sheet of glass on rollers in a factory production line

Glass was originally discovered by chance. Extreme heat from natural sources like volcanos or lightning combined with the required materials to produce glass.

Humans discovered this material, learned to reproduce it and turned it into a pottery and jewelry mainstay from about 3500 BC onward.

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For more information about how glass was discovered by accident and then turned into a material man could produce, check out our Glass History page.

In the modern era, glass has become a core building material of items large and small. It makes up windows, mirrors, windshields, screens, light bulbs, and more, so its importance is hard to overstate.

Producing it doesn't require the happenstance of the past, thanks to factories, manufacturers and professionals across the globe.

The secrets to making glass have long since been revealed and turned into standardized processes.

The Ingredients that Go into Making Glass

Large piles of sand outside a factory

Heat, (a Lot of It!) Plus 3 Natural Materials

It's possible for glass to be naturally produced by the environment. (This is how it was originally discovered.) Volcanic eruptions can turn the right minerals into obsidian, a natural glass known for its glossy dark color.

Heat is the prime ingredient in making glass, though it can take as much as 1700 degrees Celsius to make anything happen. In addition to heat, there are 3 main ingredients needed to make glass.

Sand, Sodium Carbonate & Calcium Oxide

  1. Sand: sand is the main ingredient, largely because of the silica it holds within. Silica forms the backbone of glass while helping to lend it hardness, but the drawback is that it has an extremely high melting point of 2000 degrees Celsius.
  2. Sodium carbonate: the second ingredient, sodium carbonate, helps tend to that. By lowering silica's melting point to half of what it would normally take, the glass-making process becomes much easier.
  3. Calcium oxide: the downside is that it makes the finished glass water soluble, so the calcium oxide extracted from limestone nullifies that effect.

Other Materials can also be Used to Change Glass Properties

It's possible to change the properties of the final glass product by using other elements and chemicals as additives.

  • Iron: Using iron creates glass that can absorb infrared energy and heat, which makes it a good fit for filters in movie projectors.
  • Lead: Meanwhile, adding lead to a mixture leads to glass that creates stronger reflections, and can be cut more easily.
  • Other oxides: Depending on the oxide used, it's even possible to give glass a range of different colors for various bottles' use.

The Glass-Making Process

Glass furnace heating glass ingredients

Gathering and melting the ingredients is only part of the procedure. Manufacturers can take the molten materials and work with them accordingly, depending on the end product needed.

Common Variations in Making Glass

They can either pour the melted mix into molds for making various types of containers, or they can dispense it onto vats of molten tin metal to make flat sheets. This is called the float glass method.

The Float Glass Method for Making Flat Glass Products

The float glass process is carried out via a long and continuous line of machines.

  1. Raw and recycled glass is first heated during several heating stages while impurities get removed. While this step can take as much as 50 hours, it's also a way to ensure quality as well as add ingredients that change the product's properties.
  2. The molten mix that results is poured onto the molten metal, where its thickness is controlled by how long it's allowed to settle.
  3. After that, chemical vapors are used to coat the glass to change its appearance and properties.
  4. The cooling process follows, and once completed the glass is inspected by lasers to detect and remove problem areas.
  5. If it passes, then diamond wheel cutters will move in to slice the glass and create a properly-sized final product.

Using Heat and Compressed Air for Making Hollow Glass Items

While the float glass method is a good fit for making flat products, there are other ways to make specific items like bottles, jars, light bulbs, and drinking glasses.

By pressing molten glass into a mold and cooling it to maintain its shape, heat and compressed air can make the glass push against the mold's sides. In doing so, the shape of the item can be realized and maintained.

An extra round of reheating removes stress from the new glass product while preventing it from breaking, and then the product is cooled in a temperature-controlled kiln.

While it's possible to create glass products by blowing into a traditional pipe and mold, modern machines can make as many as 600 bottles per minute.

So How Does This Apply to Auto Glass?

Modern windshields are made by taking multiple sheets of glass created with the float method and then laminating them into their final shape using heat and compressed air.

This provides the strength they need to not shatter into many pieces when you're on the Loop 202 headed home to Chandler and a semi truck ahead of you throws a rock into your windshield!

To learn more, check out our How Windshields are Made page.

A Versatile Material that is Customizable by Changing Ingredients or Manufacturing Processes

A group of different decorative glass bottles in a kitchen

Part of what makes glass such a valuable resource is its versatility. Not only can it be used in various ways, but it can be custom-made to fit the needs of a client or manufacturer.

By changing the ingredients and the various steps of the process, manufacturers can create glass with all different kinds of properties, from size, to shape, to color, to hardness and more.

Glass may not seem like much at a glance, but it's hard to imagine a world without it!

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