Monday, September 24, 2012

Telecommunications Relics

QUESTION: I recently purchased a box of glass insulators, like the kind used on telephone and electric poles. A couple of little white specks in the glass. I bought them because of their beautiful colors, but do these things have any value as a collectible? And just how were they used?

ANSWER: There’s nothing like the beauty of colored glass, especially when placed in a window where the sun can shine through it. Many people collect these glass electrical insulators for just that reason. But some, especially retired linemen, collect them because they’re a part of the history of telecommunications.

Ezra Cornell invented the insulator in 1844 as a means of protecting electrical wires front the elements and reducing the loss of current from the wire to the ground. As technology developed, power and telephone companies needed more insulators.

The earliest insulators had unthreaded pin holes. Because linemen simply pressed them onto a wooden pin, extending upwards from the crossarm of an electric pole, they didn't stay on very well since the wires contracted and expanded in the heat and cold. When Louis A. Cauvet improved the insulator by patenting the threaded pin hole type in 1865, he sold his invention to Brookfield Glass Company of  Brooklyn, which remained a major producer of insulators until 1922.

Though threaded pin holes helped insulators stay put, moisture still presented a problem since wet glass served as a conductor. In 1893, the Hemingray Company, another major manufacturer, obtained a patent for insulator "drip points." These bumps, which line the outside bottom rim of the insulator skirt,  helped prevent shorts by causing moisture to drip off. The earliest points were sharp but these were easily broken, leading to the manufacture of more rounded ones. Hemingray must have discovered that these really didn't work, since they eliminated them from later models. However, other companies continued to make insulators with drip points.

Porcelain insulators began to replace glass examples in the early 20th century, particularly on high voltage lines since glass insulators only worked on lines handling up to 60,000 volts.. By the late 1940s, only a few producers of glass insulators remained, by 1969, Kerr Manufacturing was the only company still making them.

Manufacturers produced glass Insulators in a variety of colors and types of glass. They used remnants of window or bottle glass for earlier ones. Most companies made insulators only as a sideline,  pressing them out of whatever kind of glass happened to be available. Because of this, objects like nails, screws, coins, and bits of furnace brick would get mixed into the glass. Collectors call the little white furnace brick bits rocks. Some makers, like Hemingray, would cull out these blemished pieces, but others like Brookfield Company would just sell the blemished pieces along with the good ones.

The most common insulator colors are clear and light bluish-green or aqua. Other colors include sun-colored amethyst, green,  milk glass, royal blue, cobalt, amber and Carnival glass. The only color not made in glass is red, because red requires gold as a colorant. The most popular colors are royal blue and cobalt, with amethyst a close second. Insulator makers originally produced purple ones, ranging from  light lavender to deep amethyst, from clear glass. Manganese, used to clarify the glass, turned the glass purple after being exposed to the sun’s ultraviolet rays. After the start of World War I, manganese became scarce since it was needed for arms production. Manufacturers switched to selinium, which the sun turned to the color of wheat.

Common clear and aqua insulators sell for as little as a dollar each. But prices climb steadily for rare ones such as the Buzby or the Twin Pin. Aqua ones made by the Jeffrey Manufacturing Company can sell for as much as $125 each while a threadless Canadian insulator, also known as a snow cone, can sell for about $2,000.

For more information on glass insulators, go to

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