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Making Window Glass by Hand: Crown & Cylinder Glass

All About Glass

Glass crown disk

When you think of a window, you think of a flat piece of glass. But window glass didn’t always start out flat. It once began as a massive bubble on the end of a glassblower’s pipe.

To flatten the bubble, the glassblower could spin it rapidly into a huge disk called a crown. After it was cool, the uneven, distorted disk was %%cut%% into small panes.

If, instead, the glassblower swung the bubble over a pit, he could stretch and elongate it into a cylinder. When the glass cylinder was cool, it was %%cut%% lengthwise, then reheated and flattened. Larger panes could be made this way, but the glass was still distorted—and the work was just as exhausting.

Does Window Glass Flow?

Does glass flow?

Some centuries-old window glass is thicker at the bottom than at the top. Is that because the glass flowed down over time?

No! Scientists have calculated that at room temperature it would take millions of years for glass to flow even a microscopic amount.

Older windowpanes have an uneven thickness because they were cut from uneven, handmade glass. The large glass disks made by the crown method, for example, were thicker in the middle than at the edge. Glaziers usually installed the thicker, heavier part of the pane at the bottom for stability.

Pushing the Envelope

1851 Crystal Palace
cylinder glass

All 245 designs had been rejected when horticulturist Joseph Paxton submitted his radical, last-minute entry. It would become the most magnificent glass and iron structure ever built—the main exhibition hall of the first world’s fair.

The task was enormous. The monumental building required 300,000 panes of glass, one-third of England’s annual production. Each pane, made by hand using the cylinder process, was—as Paxton had demanded—a foot longer than had ever been made before.

The Crystal Palace was erected in London’s Hyde park in 1851. Architecture has never been the same. The humble light-admitting glass pane had been transformed into a striking architectural material that captured the world’s imagination.

The Corning Museum of Glass
This article was originally published in Innovations in Glass, 1999, pp. 10–11.

Published on October 20, 2011