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  • Jon Trevillyan

The Growing Panes of Glass: A History of Glass Windows

Posted on Mar 01, 2017

Glass is everywhere. It follows us in every ritual of our lives, encasing us and aiding us. We are cocooned by it when driving, working in the office, or relaxing in the sunroom. We sip from it in the kitchen, we peer into it in the bathroom, and we put it in our shopping carts at the food market.

Perhaps the most overlooked glass, is the glass in our windows. It is the unseen medium through which we experience our world. We see, feel and hear our environment in the flash of a bird’s wing, in the rattle of the wind, and in the soothing of a sunbeam.

Without glass in our windows, our homes become places of the past: log cabins, shacks, huts—even caves. Though glassmaking is ancient, it has only been in the recent past that the art has been perfected. Don’t take for granted the art form that has made this wonder ubiquitous today.

How Old is Glass?

Ancient Egyptian and Roman civilizations knew the art of glassmaking. The Romans mastered the art well enough to put it in their windows. But in the Middle Ages, the art was only used by the church and royalty. Glassmaking was expensive and the art form wasn’t widespread at the time.

Those who couldn’t afford glass in their windows used shutters, animal hide and oilcloth. They balanced keeping the elements out with letting the light in.

Glass for the Home

Glass windows started appearing in wealthy households in the 1500s. Windows had small diamond shaped pieces of glass fitted between lead lattices. Because the lead was soft, it was often reinforced with iron.

Crown Glass

Eventually “crown glass” became popular. This method made larger panes of glass possible. First, glass was shaped into a globe on the blowpipe. The bottom of the globe was cut-off and the remaining circle or “crown” was reheated in the furnace, making it more flexible. The glassmaker then spun the hot glass. This glass disk was smooth and clear except for the center. It “swirled” and was more opaque, creating a “bullseye.” (See picture* below.)

The Cylinder Method

Next, glassmakers used the cylinder method. This was a breakthrough in the search for creating longer, flatter pieces of glass. First they made long cylinders on their blowpipe. Next they sliced the cylinders vertically, and lay them flat in the furnace to smooth them out. This method made larger panes of glass possible, though the end result wasn’t perfect.

The Drawing Method

By the early 1900s, glassmakers made large panes of glass using the drawing method. They immersed a slotted mold into molten glass. The molten glass came up through the slot and cooled on a roller that flattened it horizontally. Surface imperfections were ground and polished away.

Float Glass

In the 1950s, Alastair Pilkington pioneered a method that dramatically changed glassmaking. In this method, glass floats on a bed of molten tin. As it spreads, glassmakers are able to precisely control its thickness. The tin and glass never coalesce and the finished product is almost perfectly smooth. The large sheets of glass are cut to customized sizes and finished with a variety of glazes.

The next time you look out your windows at the office, enjoy downtime in your sunroom, or working in your greenhouse, take time to enjoy the wonder of the glass you are looking through. Its evolution has changed the way we experience our world.

Want to enjoy the glass you are looking through more? Bethany Associates offers professional window cleaning, as well as pressure washing and awning cleaning. Let us help you make your glass shine today. Call us at 888-601-4257 for a free estimate and we will be happy to serve you!

*By böhringer friedrich (Own work) [CC BY-SA 2.5 (], via Wikimedia Commons

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