Ask any housewife what she thinks of when the name "Pyrex" is mentioned, and the answer will be ovenware and kitchen utensils. Ask a chemist, and it will be laboratory glassware. Ask an insulator collector, and the answer will be beautiful carnival glass insulators.

Corning Glass Works, of Corning, New York, known the world over, was a well established company when pole-line insulator production began in 1926. (One Corning source sets the date as 1926, while another claims 1923.) At this time porcelain insulator production was well established in the power distribution field, as glass was losing popularity. The use of glass in high voltage power transmission had created a very bad reputation. To remedy this, Pyrex claimed that "the introduction of Pyrex insulators occurred in 1923, and marked the start of a new era in power transmission." They went further to claim that their new insulators had a high resistance to heat, low coefficient of expansion, were supposed to be very resistant to the effects of power arcover, and various other remarkable claims. "The glass was transparent to the rays of the sun, and would not heat excessively in summer, thus avoiding thermal shocks that had caused trouble with porcelain and earlier glass designs." "All Pyrex insulators are made in one piece, without cement or glaze. Chip or break a Pyrex insulator and the surface you reveal is exactly the same as the original outer surface." Obviously, this is not the case with porcelain, as a fair sized chip in the glaze seriously impairs its insulating ability. The early catalogs made these claims and more. The earliest catalog showed only six pin-type insulators. By 1931 it had increased to fifteen styles, covering from telephone service to a 70,000 volt power line style.

Pyrex insulators were produced in steel molds, "and the high cost of such tooling probably was the cause of the limited number of designs that were offered." The ones that were made are examples of quality materials and fine workmanship. Even though the insulators were finely made, many power styles, especially the larger types, were subject to internal strains. Despite careful "heat treatment", this annealing process caused brittleness while in service. "Some Pyrex lines were extremely good; others disastrously bad." This writer has observed several Pyrex lines in Florida and Georgia still in regular service, spotted with many porcelain replacements.

According to Sand and Imagination, a small book telling of the accomplishments of Corning, "in 1926, Corning began producing glass insulators for phone and power lines and soon was faced with the problem of radio static." Through much research by Corning scientists, it was found that the radio noise was caused by a build-up of high voltage electricity on the insulators. The power discharged when it reached a peak. "Like natural lightning, it created radio static."

To combat this problem, a conductive coating of tin oxide was sprayed on the arcing surface. "The two scientists found that it allowed electricity to leak noiselessly off the insulators. By 1928 Corning was producing insulators with an electronic overcoat, and radio audiences found the listening better." This is what is commonly called "carnival glass" by collectors. Eventually, it was found that this sprayed on coating, so thin, tended to deteriorate. As this colorful coating disappeared on many insulators, "islands of conductivity" were left. Sparks occurred from island to island to such an extent, that after a short time, the radio interference characteristics of these treated insulators were worse than that of untreated ones."

Although Pyrex is so well known for its pin-type insulators, its contribution to radio insulators is important. Corning offered various different styles of Pyrex glass insulators for radio transmitting and receiving. The smallest, being 3-5/8 inches long, was commonly used for home sets and other equipment not over 250 watts (radio power). The 7-1/2 inch size is used on 1,000 watt sets. Another all glass insulator is 12 inches long, used for powerful transmitters. Corning made antenna insulators as long as 19 inches, and ones possibly longer. These were straight, heavy walled glass tubing with metal fittings on each end. Many Pyrex antenna insulators include the Patent number: 1700066. This is a patent issued for a special glass that has rather low losses on radio frequencies. Patents issued to Corning for antenna insulators as well as pin-types were generally for their improvements in the glass formula. Stand-off insulators were also made for lead-in transmission lines to radio equipment. These are glass rods (one inch diameter) with a metal base and a screw top. It stood vertically, with the line fastened on top.

Pyrex insulators are found only in clear, straw (light yellow), and metallic salts coated -- radio treated (carnival glass). It is my belief that Corning produced most all of their powerline styles in carnival at one time or another, but it is not known for sure. Also there are a few styles that have been listed in their catalogs, but have yet to be found. Corning also claimed to offer brown (or amber), as a marker type, in the smaller sizes. I haven't seen or heard of any in this color.

According to Brent Mills, author of Porcelain Insulators, Corning went out of the insulator business sometime during World War II. He goes on to explain how they sold their insulators below the current market price for porcelain, and received a great deal of Government business. Due to a great number of field failures, especially in suspension insulators (sombrero), and war pressures, they went out of the insulator business.

On the following page is a list of Pyrex insulators either known to exist or listed in catalogs:

Note: Pyrex 701 is the largest single piece, pin-type glass insulator that has ever been molded in the United States, weighing in at 38 pounds.