Types of Glass Production: Cylinder & Crown

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.

Before modern mechanical processes, how did people make window glass? What did it look like? In this lesson, explore methods of glass production called cylinder and crown.

Basics of Glass

Have you ever looked through the windows of a very old building, one built in the 16th or 17th century? Did you notice a wavy uneven appearance in the glass? That's because these panes were made by hand. Today, most window glass is made by modern processes on large machines, so it's flat, clear and of uniform thickness. But that wasn't always the case. For thousands of years, glass was made by heating ingredients to a very hot temperature and then using tools to blow the molten glass into desired shapes. In this lesson, we'll discuss two processes for making window glass. But first, let's cover some basics about glass.

Glass is an interesting material. It's hard but has flowing surface properties. It looks like a frozen liquid. In fact, it's a type of substance called an amorphous solid which has properties of both a solid and liquid. It's made by heating sand and other additives in special ovens to very high temperatures, as much as 1700 degrees Celsius. When the substances melt, they form glass. This allows glass to be blown into shapes when it's still a hot liquid.

Examples of English glassblowing skills and tools
Images of English glassblowing

To blow glass, a person called a glassblower, who works with a long hollow steel pipe, gets a blob of molten glass from the furnace. The blob of glass, by the way, is sometimes called a gather or a gob. Then they blow the glass and work it in specialized ways to a desired shape, using many techniques. Now let's discuss two of those techniques, processes called crown and cylinder glass.

Making Crown Glass

Crown glass is the older of the two, so let's look at it first. The process to make crown glass was possibly invented in Syria. By the 14th century, it was being used in Europe, where French glassmakers perfected it. To make crown glass, blowers took a gob of molten glass and blew it into the shape of a very large balloon. They then flattened the balloon, transferred it to a solid metal rod and spun it very quickly so to create a large flattened disk. The disk was then cooled and cut into individual panes of glass.

Blowing and flattening the disk in the process of making crown glass
Making crown glass

Crown glass disks had uneven surfaces and varied thickness. The best window panes were cut from the outer edges of the glass disk, where the glass was the thinnest. The center of the disk of crown glass had a circular notch in it from where it was detached from the blowpipe. This was called the 'bullseye' and sometimes used for decorative purposes. Today, you'll occasionally see it, or reproductions of it, on buildings made to look like they're old.

Making Cylinder Glass

Crown glass enabled buildings to have glass windows, but the process had its limitations. The glassblowers couldn't make extremely large glass disks, and those disks were cut into small panes of glass. Eventually, another method was developed from which much larger panes could be made. That method was called cylinder glass, and it developed at some time in the very late 1700s or early 1800s. From then on, through the beginning of the 1900s, it was the way most window glass was made.

Cylinder glass begins in the same way as crown glass. The glassblower gets a gob of molten glass on the end of his blow pipe. But then, instead of a balloon shape, the glass is blown into a shape like a large long bottle. A very long bottle. The men who made this type of glass (and they were mostly men) stood on a high vertical platform and blew the glass into a deep trench. This allowed them to create the very long cylinders, which were ideally at least around one foot across in diameter and five feet long. Imagine trying to blow a piece of glass that big!

Glassblower standing on a platform, blowing a cylinder of glass
Making cylinder glass

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