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]

Old Woodworking Machines

Old Woodworking Machines

This collective website, which started as an online discussion forum, now also includes a large database of manufac… [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    

Rare Cd731 Threadless Insulator In Dark GreenVintage Cobalt Blue Embossed Insulator - 1893 Hemingray Petticoat - Cd 162Boston & Maine Railroad Ameythest Insulator Cd 304/310 Hemingray "coolie Hat" Antique Power Insulator Vnm Rare!!Threadless Stove Pipe Threadless Civil War InsulatorE.c.& M Co. S.f. Nice Insulator Exceptional Beveled Dome E.c.m.co. S.f. Early Telegraph InsulatorAntique Electric Glass Insulator W/bracket-marked Patent Date Aug. 20, 1851Cd 248/311/311 Hemingray No. 79 Three Piece Stacker Power Insulator Rare!!145 Bright Yellow Green AmericanHemingray #0, Provo Type Cd-249 Medium Aqua Glass Insulator ExcellentBlue Aqua Hemingray Muncie Two Piece 14 Lb. Glass InsulatorHemingray #43 Cd-214 7-up Green Glass Insulator MintNeat Crude Threadless Old Mcmicking / Victoria Bc Canada Glass Insulator 1875Cobalt Blue Hemingray19 & Amber Petticoat InsulatorsHemingray Muncie Type Railroad Electric Insulator Blue Glass May 2 1893 & BaseRare Brookfield Glass Insulator Cd 126 [430]Hemingray Montana Stacker #79 Cd-248 Medium Aqua Blue/green Glass InsulatorPorcelain Cable Insulator & Cobalt Blue Spool Insulator Cd 267 ?Beautiful Glowing Orange Amber Cd 162 Hemingray Petticoat Signal InsulatorGlass Insulator Corn Flower Blue Mclaughlin-20 Cd 164 Rdps MintRare Teal Blue / Green Glass 19thc Lightning Rod InsulatorDeep Cobalt Blue Insulator, Hemingray -19 Cd 162 Beautiful Bubbles & CharacterHemingray Cd 248/311/311 No. 79 Three Piece Glass InsulatorTrue Green Manhattan Dated Cable InsulatorBeautiful Dark Orange Amber Cd 162 Hemingray No 19 Signal InsulatorCd 154 Whitall Tatum No. 1 "purple" Sca Antique Glass Telegraph Insulator Mint!!104 Nn Teal Green Pennycuick With Some Amber StreakingCd 104 No Name "pennycuick" Teal Aqua Antique Glass Telegraph Insulator Rare!Telephone Pole Glass InsulatorsFort Wayne Electric Co Cd-162 Light Aqua Glass Insulator ExcellentAntique Glass Insulator Hemingray No 2 Transpostion Pat May 2nd 1893 Cd 201 Glass Insulator Back Wards N / H.g. Co. Petticoat Cd 145 Crude SatinPurple Whitall Tatum #1 Glass Insulator - Near Mint Cd 162 Hg Company Powder Blue Insulator Full Of Snowflake & BubblesCd 145 W. Brookfield "creb" Shop #10 "yellow Green" Antique Glass Insulator Wow!Stunning Antique Houze Slag Glass Swirl Auto Ashtray Insulator Model A Model TAntique Glass Insulator "unusual"Antique Vintage "whitall Tatum No 1" Purple Glass Insulator Telegraph Pole #ls18Antique Glass Insulator Telephone Telegraph S. B. T&t Co. Lt. AquaMixed Lot Of 15 Glass Insulators Hemingray Dominion1800's Lightning Rod PairAntique Glass Insulator C.g.i.co. Cd 102 Rosey Purple. Nice!Hemingray Insulator "mickey Mouse" Estate Sale FindInsulator Dominion-42 (r-skirt) ['d' In A Diamond] Honey AmberVvnm Purple Whitall Tatum Cd154 Cd 213 Hemingray No. 43 "two-toned" Antique Glass Telegraph Insulator Nice!Rare Aqua Glass Battery Rest Insulator - E. S. B. Co. - Large SizeBrookfield #10 Olive Green Glass Insulator With Amber Streaks On Dome Cd1014 Dif Neat Old Grey Porcelain Power Distribution Insulators Thomas Incuse & NnCd 161 California Sage Green Antique Glass Telegraph Insulator Very Nice!!4 Dif Neat Old Locke Porcelain Power Insulators "roman Helmet" Style W/ EarsHemingray-60 Mickey Mouse. Nice BlueDark Emerald Green Star Beehive Insulator Shooting Star Bubbles & Mold MarkingsCd 102 Diamond "pony" Antique Canadian Glass Telegraph Insulator, Olive Green!!Cd 102 Star "green Amber" Antique Glass Telegraph Insulator, Wonderful Color!!Cd 210 Postal "vertical Bar Sdp" Antique Glass Telegraph Insulator Super!!Purple Cd-145 H.g.co. PetticoatVintage Purple Glass InsulatorCd 102 W. Brookfield "arc Embossed" Light Green Antique Glass Insulator Rare!