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”)

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

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

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



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]



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    

Cd 151 Cornflower Blue InsulatorCd 132 Glass Insulator Clear, Gray, Purple Tint, Patent Dec. 19 1871Chartreuse Green InsulatorInsulator - Carnival Hemingray Cd 162Blue Cd 267.5 Boston Subway InsulatorLynchburg No. 36 Made In U.s.a. Olive Green Glass Signal InsulatorCd 110.5 Nat. Insul. Co. Glass Insulator Aqua Base EmbossedPurple Amethyst Electric Insulator B.g.m. Co.Cd 162 Signal Glass Insulator In Dark Peackock Blue!Cornflower Blue Duquesne InsulatorRainbow Carnval Cd 320 Pyrex T.m. Reg. U.s. Pat. Off. Made In U.s.a. InsulatorCd 126 Glass Insulator Green, Light Green, Crown Embossed Brookfield CrebDark Blue Aqua Cd 267 No. 4 Cable InsulatorCd 131.4 Glass Insulator Aqua L.g.t & Co_ Pat Jan 25 1870 Pat Feb 22 1870Cd 256 Manhattan Glass Insulator Green Aqua With Amber Patented June 17 1890 Cd 257 Hemingray Mickey Mouse Glass Insulator In Hemingray Blue!Yellow Green Star Glass Insulator Leaning To ChartrueseBeautiful Hemingray Insulator Dark Honey Amber Glass D-512Monster Dome Glass Cd 126.4 We Mfg Co Patent 1871 Wu Old Telegraph InsulatorAqua Cd 24 The United States Light & Heating Co Battery Rest InsulatorCd 128.4 Hemingray Big Mouth Glass Insulator With Yellow Tint!3! Beautiful Cd-154 Vintage Glass Insulators...hemi Blue, Purple & Lt. GreenRare Purple Braille Keg InsulatorCd 202 Hemingray Blue Glass Insulator Near Mint!Antique Aqua Blue Green Glass Cable Insulator Roman Helmet Mickey Mouse EarsCd 161 Purple California Glass Insulator Near Mint!S.b.t & T. Co InsulatorAntique Turquoise Aqua Glass Telegraph Electric Insulator No NameCd 162 Hemingray Signal Glass Insulator In Sapphire Blue!Aqua Cd 283 Hemingray No 1 “provo” Type Patented April 25 1899 InsulatorCd 121 Royal Purple Glass InsulatorOld Otis Lightning Rod Insulator With Metal PointW. Brookfield Cd-116 New York Dark Aqua Glass Insulator MintGnw Tel Co Insulator / Purple And ClearLight Purple Rose Colored California Antique Glass Telegraph Insulator VintageAqua Cd 302 Hemingray Patent May 2nd 1893 Muncie Type Insulator2 Old Metal Glass Insulator Holders, Mounts, FletcherNice! Cd 257 Old "mickey Mouse" Hemingray 1890 1893 Power Glass InsulatorCd 145 Glass Insulator In Deep Jade Green Milk - Mint!Dark Aqua Cd 254 No 3 Cable InsulatorBlue Cd 36 No Embossing Battery Rest InsulatorStunning Bluish Gray U-663 Thomas Porcelain InsulatorHemingray Coolie Hat Insulator Cd 304/310 Blue Aqua Nice!Gorgeous Carnival Glass Pyrex Cd-235 Vintage Glass InsulatorVintage Ceramic And Glass Electrical InsulatorsPurple California Cd 161 Glass InsulatorDark Olive Root Beer Amber Cd 102 Diamond InsulatorDark Green Colored Mcglaughlin 20 Antique Glass Telegraph Insulator VintageNeat! Pat'd Nov. 23rd 1886 Threaded Glass Mine Insulator...lookInsulator - H.g. Co. Cd 196 - Nice!Hemingray Cd-257 Green Aqua Mickey Mouse Glass Insulator...nice!Hemingray Muncie Insulator Cd 303/310 Aqua Nice!Insulators Cd117 No Name & Insulator With Amber Swirl - Bits Of DebrisAqua Cd 169.5 Brookfield Insulator Glass Insulators"mighty Fine" Hemingray "mickey Mouse" Power Glass Insulator W/ Fangs & Fizz!Miva Bf2m Cd-677.3 Off Clear Glass Insulator ExcellentCd 102 Purple Glass Insulator Near Mint!Royal Purple Cd 102 Vertical Bar 'diamond' Blot Out Pony Insulator7-up Green Colored Mcglaughlin 20 Antique Glass Telegraph Insulator Vintage