Genie in the Bottle: Glass Bulbs & TV Tubes

Genie in the Bottle: Glass Bulbs & TV Tubes

In 1879, the brilliant inventor Thomas Edison was on the verge of a breakthrough. He had discovered a slow-burning filament that would glow for hours in the vacuum of a glass globe. But to create the first practical electric light, he needed a glass globe that would not implode when the air was drawn out. Edison asked for help.

At Corning Glass Works, glassblowers painstakingly shaped bulbs that could stand up to the new technology. The world’s desire for electric light required a more efficient process. A young shop assistant began experimenting, blowing into glass and letting it drop from the end of an iron. Together, air, heat, and gravity shaped the glass into the right bulb form. Glassblowers could now produce thousands of bulbs a day. But they still couldn’t keep up. What was needed was a machine to produce thousands of bulbs in a minute.

In 1922, William Woods, a former glassblower, experimented by holding a shovel with a hole under a stream of glass. As the glass sagged through the hole, it formed the perfect shape for blowing a bulb. Woods realized that a ribbon of glass sagged through holes into moving molds could be shaped and blown mechanically into bulbs. The ribbon machine he designed is still state of the art—and still the fastest glass-forming machine ever built.

Spinning a Rectangle

The earliest television bulbs were small, round, and made by blowing glass into molds. Later, the bulb’s funnel and faceplate were pressed separately, then sealed. As TV-tube bulbs got larger, it became difficult to join the thick, heavy funnels to the faceplates. There was no way to press a thin glass funnel.

At Corning Glass Works, James Giffen, a farmer turned glassmaker, had been asked to make a casserole dish by spinning glass in a mold. Giffen soon realized the shape of the casserole was wrong for spinning, but the TV funnel was the right shape. He dropped a glass gob into a spinning mold. Centrifugal force caused the glass to flow up the sides, creating a thin, lightweight funnel.

When the TV industry needed a rectangular bulb, experts said it would be impossible to make the shape by centrifugal spinning. Giffen ignored them. He studied how the glass flowed, redesigned the mold, and spun the glass into the new shape.

Published on October 25, 2011