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Types of Glass Production: Rolled & Flashed

Instructor: Stephanie Przybylek

Stephanie has taught studio art and art history classes to audiences of all ages. She holds a master's degree in Art History.

Glass is all around us in windows, drinking vessels and decorative pieces. But did you know there are many ways to make glass? In this lesson, explore rolled and flashed glass production.

What is Glass?

We use glass for many things and it can be made in several ways. We're going to look more closely at two methods of creating glass that can be used for decorative and practical purposes.

But before we discuss manufacturing specifics, let's review basics. Fundamentally, glass is sand that's heated to a very high temperature. Most commercial glass today contains sand, bits of recycled glass, soda ash (added to reduce the melting point), and limestone, which mitigates reactions caused by the soda ash. These materials are mixed and heated until they melt, turning into glass.

If you think about it, glass has unique qualities. It's hard and can be brittle, but has a smooth and flowing surface much like a liquid. Actually, it's an unusual material known as an amorphous solid, a substance that combines qualities of solids and liquids. You can add different substances to glass to give it certain qualities. For example, elements like copper and gold are used for color, or additives can make it ovenproof.

Now that you know what glass is, let's explore two methods of making it.

Rolled Glass

A type of glass called rolled glass is made by pouring molten glass (as hot as 1050 degrees Celsius!) on a steel sheet and flattening it with a large heavy metal cylinder called a roller. After it's rolled, the glass is water-cooled to around 850 degrees Celsius and then annealed, or allowed to cool to room temperature very slowly in a controlled environment so it doesn't cool too fast, which can make it brittle. Some rolled glass is made on a double roller table, which presses the molten glass between two rollers. The thickness of the glass can be adjusted by changing the gap between the rollers. Rolled glass tends to have a patterned surface, and it's not completely flat or transparent. Flattening the glass with a double roller creates a glass with a more even surface.

One type of rolled glass is called obscure glass. It has a pattern pressed into its surface and is used for both decorative and privacy purposes. Rolled glass is used for art and architectural purposes. People who work with contemporary stained glass are sometimes using flat segments of glass made with the rolled glass process.

Flashed Glass

Another method of making glass results in a product called flashed glass. Flashed glass is blown from two kinds of glass, a base of clear glass and an outer thin layer of colored glass. Here's how it's done. Using a long steel blow pipe, a person gathers a blob of molten clear glass on the end of the pipe, and then dips that blob in molten colored glass. They then blow into the pipe and expand that glass into the desired shape. This spreads a very thin layer of colored glass over the clear surface.

Flashed glass picture with cut decorations, allowing the clear glass to show through
Example of flashed glass

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