Insulators were originally designed to keep the wires linking telegraphs and telephones insulated from the wooden poles that held them aloft. In conjunction with the expansion of rural electrification in the early 20th century, there was a major boom in the manufacturing of insulators, peaking from the 1920s through the 1940s with production in the millions per year.

Commonly made from glass or porcelain in a dazzling array of shapes and colors, including amber, cobalt blue, olive green, and royal purple, insulators are prized for their rarity and physical beauty. In collector’s circles, clear and aqua shades are considered generic because they result from the natural iron content present in most glassmaking materials. Some insulators were embossed with a manufacturer’s name and style number using engraved molds, yet many insulators were produced without any markings whatsoever.

The earliest insulators were non-threaded “ram’s horn” and “glass block” designs, developed simultaneously with the growing telegraph line network initiated in 1844. Soon the pinhole or pintype style was established, allowing a glass insulator to be attached atop a wood or metal pin using cloth coated in a tar-like substance. Threaded insulators were first patented by Louis Cauvet in 1865 as a means for more securely fastening the glass objects to the tops of wooden pins. This design is still considered standard for electrical insulators today.

Use of porcelain and ceramic insulators spread during the late 19th century alongside higher-voltage electrical wires, like those required for home power lines, because the protective properties of porcelain proved superior to glass. Porcelain insulators were produced in a variety of colors to imitate their glass counterparts, ranging from deep blues and chocolate browns to bright yellows and greens.

Insulators are typically identified by manufacturer, including H.G. Co., Pyrex, Brookfield, and Hemingray, as well as the Consolidated Design (CD) coding system. CD numbers describe the production location and shape of pintype glass insulators, with 10 – 99 representing battery rest insulators, 100 – 375 for North American threaded insulators, 376 – 699 for all foreign insulators, 700 – 799 for North American unthreaded insulators, and 1000 – 1199 for all other miscellaneous styles, including glass blocks, spools, and dead-end insulators.

Within these broad categories, shapes are broken into many different variations describing the number of petticoats, drip points, skirt styles, wire grooves, and other features. Favored North American designs include the “Mickey Mouse” shape with two protruding glass ears and a saddle-groove form, as well as those made in lustrous carnival glass. The French created a distinctive “Gingerbread Man” form, with a rounded top and two pointed, upturned arms. The “T-Bar” design was also popular in Europe, and features outstretched, grooved arms, sometimes made with a square top, creating a robot-like resemblance.

Glass insulators were designed in a few basic forms depending on their specific electrical application. “Pony” insulators, often no more than 31/2 inches in height, were used for...

One of the most prolific insulator manufacturers in the U.S. was the Hemingray Glass Co. Incorporated in 1870, the firm operated factories in Kentucky and Indiana, where it also produced other glass items, like bottles, fruit jars, kerosene lamps, and glassware. Hemingray created the largest stylistic variety of any manufacturer and purposefully designed colorful insulators, as opposed to the typical practice of recycling leftover batches of colored glass. The company's famous Hemingray No. 42 remains the best selling insulator of all time.

About our sources | Got something to add?

▼ Expand to read the full article ▼

Best of the Web (“Hall of Fame”)

Hemingray.info

Hemingray.info

Christian Willis' well-organized database of Hemingray insulators. Browse over 300 photos by CD number, style, or s… [read review or visit site]

Hemingray.net

Hemingray.net

Shaun Kotlarsky's tribute to the Hemingray Glass Company. While known for its insulators, this site also showcases … [read review or visit site]

Insulators.info

Insulators.info

Bill Meier's reference site by and for insulator collectors includes event listings, reference information, photo g… [read review or visit site]

Glassian

Glassian

For an explosion of color and a quick education on the many beautiful varieties of insulators, blown glass bricks, … [read review or visit site]

Alloy Artifacts

Alloy Artifacts

A tool collectors’ dream, this site is a deep repository of photos and info on 20th century hand tools and the co… [read review or visit site]

Vintage Machinery

Vintage Machinery

This collective website, which started as an online discussion forum, also includes a large database of manufacture… [read review or visit site]

Drainspotting

Drainspotting

Josh and Cam Larios have created this site enabling people to upload and 'tag' photos of historic or artistic manho… [read review or visit site]

A Millers Falls Home Page

A Millers Falls Home Page

Randy Roeder has carved out a niche for himself with his fine website devoted to the history of the Millers Falls C… [read review or visit site]



Clubs & Associations

Discussion Forums

Other Great Reference Sites

Most watched eBay auctions    

Amber Glass Insulator-double Petticoat-am Insulator Co. N.y.-1883 Pat. Purple Cd 194/195 Hemingray - 54 A - B Two Piece Transposition Insulator Cd162 Glowing Dark Cobalt Hemingray SignalAqua Withycombe Cd 143Cd 143.5 T-h.e Co. Aqua BeehiveCd 123 E.c&mco.Dark Green Aqua Withycombe Cd 143Extremely Rare Cd 102.4 - New England Tel And Tel - InsulatorCd162 Mclaughlin Vibrant Green*rare* Floy Unusual Clean Power Insulator Cobalt Blue Cd 162 Hemingray Insulator May 2 1893 Petticoat Ein 240 NiceTwo Tone Cd162 California SignalSca Horizontal Ridged Small Beehive Shaped InsulatorCd 178 Santa Ana Purple "spaceship"Green Cd145 American BeehiveCd 154 Mclaughlin Emerald GreenCd257 Mickey Mouse Aqua With Lots Of AmberWestinghouse Choke Coil Holder With Hemingray No 2 Provo Insulator No Reserve!Cd254 Dark Yellow Green No3 CableVery Pretty Royal Purple Pony Telephone Glass Insulators "original" Not Stained!Hemingray Cd162 7up GreenRare No Drip Point Orange Gold Amber H.g.co. Petticoat InsulatorAqua Cd 256 Manhattan “patented June 17 1890” Cable Insulator Cd 135.5 Blue Blue Aqua E.r.w. InsulatorLight Blue Cd 136.4 No Embossing Canadian Boston Insulator Light Aqua Cauvets Cd 131Cd 133.1 Homer BrookesCd162 Whiskey Amber SignalAmber Two Tone Cd 162 H.g.co. Patent May 2 1893 Petticoat Insulator Cool Cd 127 Brookfield With Milky Swirls InsulatorLight Lavender Cd 121 W.f.g.co. Denver, Colo. 16 Toll InsulatorYellow Amber Cd 1070 Hemingray-109 Made In U.s.a. Spool Insulator Cd 145 Wgm PurpleBlue Aqua W/amber Cd 257 Hemingray Patent June 17 1890 May 2 1893 Insulator Beautiful Golden Honey Amber Lowex "frog Eyes" And She Ships Free!Purple Cd 145 B Beehive Insulator Purple Cd 102 Brookfield New York Pony Insulator Very Pretty! Dark Purple W.g.m.co. Cd-106 InsulatorPurple Cd 102 B.g.m.co. Pony Insulator Cd 128 Opalescent E14b HemingrayMighty Nice Mickey Mouse Glass Insulator W Free Shipping!Vintage Ribbed Honey Amber Glass Transformer Capacitor Bushing Insulator W MetalVery Nice Scarce Cd 35 Battery Rest InsulatorCd252 No. 2 Cable GreenAqua Cd 1070 Hemingray-109 Made In U.s.a. Spool Insulator Mclaughlin - 20 Cornflower Blue Glass Signal Insulator Cd 145 Royal Purple W.g.m. Co. InsulatorPurple Cd 166 A011 California Insulator Marigold Carnival Cd 235 Corning Pyrex T.m. Reg. U.s. Pat. Off Insulator Honey Amber Cd 219 Hemingray - 660 Lowex Made In U.s.a. Insulator Ec&m Co S F Cd 123 Glass Insulators 2008 Commemorative Nia Portland OregonVictor U-869a Cobalt Blue Porcelain Insulator MintVintage Glass Insulators - Aqua Blue/green 3 1/2" Tall *pristine* Deep Royal Purple G.n.w.tel. Beehive InsulatorCd. 280 Prism Insulator - RareClear Cd 190/191 Hemingray-50 Made In U.s.a. Two Piece Transposition Insulator An Attractive Lilac Cd 162 H.g.co.Vintage Hemingray Cobalt Blue Reverse Paint Glass Insulator 1893Huge Teal Aqua Locke No 17 Victor N.y. Grooved Power InsulatorHoney Amber Cd 230 Hemingray Made In U.s.a. D-512 Insulator