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What is Float Glass?

By Harriette Halepis
Updated May 17, 2024
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When a piece of floating glass is placed on top of a piece of molten metal, the final product is called float glass. This process creates a uniform piece of glass that is entirely solid. Most contemporary residential and industrial buildings are made from float glass, though this wasn't always the case.

Before the dawn of the 17th century, almost all glass panels were cut from crown glass. In order to manufacture crown glass, glass manufacturers had to create large cylinder shapes that were then cut in half and flattened to form one window pane. In 1848, an English engineer by the name of Henry Bessemer attempted to form a glass manufacturing process that was less tedious than the original crown glass process. Bessemer's manufacturing system included one large ribbon of flat glass that was rolled between two rollers.

In addition to the rolling of the glass, each pane of glass had to be polished by hand. This turned out to be a very costly manufacturing process. Numerous inventors attempted to create a more efficient system, though none succeeded. It was not until the early 1950s that Alastair Pilkington and Kenneth Bickerstaff invented a new kind of glass termed float glass.

Float glass is derived from a mixture of raw materials including sand, limestone, dolomite, and soda ash. These materials are mixed together, and then placed into an extremely hot furnace. Once the glass has reached the desired temperature, it is stabilized, and then placed inside of a molten tin bath. Due to the reaction between the glass and the molten tin, the glass eventually makes its way to the surface of the tin bath. As soon as the glass is cool enough to handle, it is passed through two mechanical rollers.

The speed of the rolling machine indicates the width and size of the glass, which is why some pieces of float glass are larger or smaller than others. Finally, the glass is placed into a lehr kiln, a temperature controlled kiln that is specially made for the glass process. The result of this entire procedure is a perfectly smooth piece of uniform glass.

As soon as a piece of glass is stable temperature-wise, it is then cut into specific shapes and patterns according to a customer's needs. Within the glass world, the float glass process is frequently referred to as the Pilkington process, since Alastair Pilkington is largely credited with the invention of float glass.

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Discussion Comments

By nony — On Jun 30, 2011

@allenJo - I’ve always wondered about those movies, and why the windows shatter that way. There may be something more to it than that, since those windows are effectively props.

I do know that plate glass is used for most modern buildings. It’s a thin sheet of polished glass which goes through a heating and cooling process to make it stronger. Sometimes they put it through the float glass process too.

By allenJo — On Jun 29, 2011

One thing to watch out for is if you ever need to drill a hole through glass. I know that’s probably not something you do often, but it is done from time to time. Some tools are designed to help you do this, but a lot depends on the quality of the glass.

For example, if you are drilling into tempered glass, you risk shattering the glass into many tiny pieces. That’s because tempered glass is treated with either chemicals or heat, and when broken, it will shatter into many tiny pieces.

Watch the movies where the actor gets thrown through the window and it shatters into millions of pieces. That’s what tempered glass does. It doesn’t just break into large diagonal fragments like regular glass would.

My word of advice is not to attempt drilling through glass unless you know what you’re dealing with.

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