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    

Ec & M Co San Francisco Cobalt Blue Insulator 1870s Rare Western GlassInsulator Aqua Cd 109 Base Embossed Chicago Insulating Company RareU.p.r.r. Cd 735 Tophat Threadless Insulator In AquaLarge Cable Top No 4 Cable Power Glass Insulator124.2 Tealish Green Tough Cd 200 Star InsulatorDark Olive Brookfield Transposition InsulatorBeautiful Corning Pyrex Carnival Glass Insulator 1 171Clean Hemingray Muncie Type Glass Huge Two Piece Insulator Rare Cd 162 (090) Hemingray Dark Orange Amber Glass Insulator *rare* Wedge Drip Point Star Pony InsulatorAwesome Dark Olive Amber Brookfield "hoop Skirt" Glass InsulatorStunning Bright Seven Up Green Cd 214 Hemingray 43 Power InsulatorCd 252 (040) Hemingray - 62 Flashed Amber Glass InsulatorSmall Glass Suspension Type InsulatorCd 211 BrookfieldPrimo! Purple Passion! Glass Insulator Not Stained Or Dyed! She Ships Free!Amber Telephone Insulator Petticoat Hemingray Pat. May 2, 1893Awesome Base Emb. Bright Blue With Milk Swirls Cd 135 Chicago Diamond InsulatorBase Embossed Chicago InsulatorClean Pretty Blue Hemingray 60 Mickey Mouse InsulatorMclaughlin No 16 Dark Or Emerald Color Green Glass Insulator UsedDynamic Two Tone Star Glass InsulatorMacomb Dome Embossed Porcelain InsulatorRailroad Ceramic Insulator Mustard? Telegraph/telephone VintageCd 257 (120) Carnival Glass Hemingray 60 Glass InsulatorDeep Royal Purple *pristine* Diamond Toll InsulatorVintage Mickey Mouse Ears Wire Insulator, Green GlassH.c. Co. Light Green 'double' Telephone Insulator May 2, 1893U-401b?? Oddball Porcelain Threaded InsulatorLarge Antique Glass Insulator W/ Fred M Locke Victor Ny No16 Embossed On Base! Mclaughlin No 16 Light Green Glass Insulator UsedSteel Blue Cd 145 No Embossing Grand Canyon Style Beehive InsulatorHobo Medicine Beaumont Texas Cobalt Blue BottleVintage Smokey Light Purple California Glass InsulatorVery Cool H.g.co Rr Signal Glass Insulator!C.g.i. Co. Light Purple Colored Glass Insulator California Glass Insulator Co.B 3 Small Threadless Spool InsulatorGreat Rainbow Glazed Speckled Porcelain InsulatorGreen , Light Blue Westinghouse & Yellow Porcelain Insulators! Good Condition! Nice No Name In Yellow Green Color Glass Insulator Pointed DomeBeautiful Medium Purple Cd-121 Toll InsulatorSquare D Dome Embossed Porcelain InsulatorRare Mclaughlin No 19 Sage Green Glass Insulator CapHeavy Triple Ridge Brookfield Blue Aqua InsulatorCd 252 (010) Patent - Other (hemingray Product) Glass InsulatorHemingray 60 Clear Glass Mickey Style InsulatorAwesome Steel Blue Cd 565.1 Russian Hemah InsulatorCrude Little Porcelain Pony InsulatorAn Awesome Blue/gray Porcelain Signal Insulator With MlodBeautiful Hemingray Cd-257 Mickey Mouse Insulator...amber Swirls In EarsUnique Bat Ears Glass Insulator From France Vvnm / Mint Cool Aqua ColorSharp Embossing Straight Sided Brookfield Cd127 InsulatorVery Nice Vintage Lot Of 5 Small Green Brookfield InsulatorsSix Very Nice Glaze Colors Of Various Spool InsulatorsTwo Unusual Beehive Type Insulators, One Is A Nat.co.Universal Patented April 12 1910 Brown Porcelain Insulator Fire Plug Hydrant OldReally Cool Medium Blue Nn Pittsburg Mlod Signal InsulatorTough Cd 202 K InsulatorCd 126[080] W. Brookfield Glass Insulator In Olive Green. Excellent Condition!