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    

Nearly Perfect Threadless Concave Skirt Wyoming Transcontinental Rr InsulatorGreat Golden Honey Amber Hemingray Railroad Signal Glass InsulatorRare L.c.t. & Co. Glass Insulator Telegraph 1870 Patented Aqua Blue Skirt ChipsAntique Purple Mickey Mouse Insulator Usa Made- California Vtg Heminray Glass Insulator Green Patent May 2, 1893 Triple PetticoatS. Mckee And Co. Threadless InsulatorBrook's Patent Ramshorn 1867 Metal And Glass Insulator*pristine* Aqua Two Piece Muncie Type Huge Two Piece Glass InsulatorSapphire Blue Cd 162 Hemingray No. 19 Insulator Hemingray 14 Insulator With Early Single Swivel Tree Bracket Both Very NiceHemingray Insulator May 12, 1891 Columbia (set Of Two)California Smokey Glass Insulator Pristine Cd 162 Hemingray-19 Green With AmberPurple W/swirls Cd 162 California InsulatorPretty Olive Green Canadian Boston Resin InsulatorAntique 1893 Hemingray Mickey Mouse Glass Insulator - Blue Green ColoredRare Antique Glass Insulator Lri Purple Tabbed Lightening Rod InsulatorNo. 2 Cable Nice Olive Amber Antique 1890 -1893 Mickey Mouse Glass Insulator - Blue Green ColoredLot Of 12 Telegraph Wooden Glass Insulator Holder Pegs Post Pins Very NiceAmber Capacitor Ribbed Glass InsulatorBeautiful Purple "whitall Tatum No 1" Glass InsulatorClear Cd 128.4 Hemingray Sb "big Mouth" InsulatorCalifonria Sca Transposition Attractive Resin InsulatorBeautiful Golden Honey Amber Frog Eyes And It Ships Free!Victor U-834 Cobalt Blue Porcelain Insulator Mint New Old Stock Private PowerRoyal Purple Cd 102 Vertical Bar Diamond Vertical Bar InsulatorVery Unusual Antique Pottery Ceramic Brown Glaze Insulator. Great Color/shape.Plum Cd 161 California InsulatorBoston Bottle Works Screw Top Resin InsulatorBat Wing Mickey Mouse Eared Cable Telegraph Insulators Aqua Blue Colored Glass Cobalt Blue W/milk Swirls Special Issue Cd 269 Style H&h Electric InsulatorNice Emerald Green Cd 152 Brookfield Insulator With AmberAmber Cd 102 Diamond over Blotted Out 'diamond' Pony InsulatorAqua Cd 112 S.b.t & Keg InsulatorYellow Green Cd 112 Lynchburg No 31 Made In U.s.a. InsulatorPyrex Stacker Vtg Insulator C10 Yellow Tint Oak Display Stand Exc ConditionThirty-one Gifts 31 Making Memories Thermal Rolling Cooler Black Parisian Pop Special Issue Olive Green No 2 Columbia L.s.v. InsulatorUnmarked Westinghouse U856a Greenish Brown Fog Bowl Porcelain Insulator Exc.Sca Califonria Cable Attractive Resin InsulatorLight Aqua Cd 190/191 A.t.& Two Piece Transposition InsulatorStainless Steel Confederate Flag Insulated Can HolderCal. Elec. Works Attractive Resin InsulatorMcmicking Insulator Cd 734, No Dot After "c" In Bc, Nice Shape, Lt Aqua.Cd-152 Hemingray Dark Olive Color Cobalt Blue Slag Glass Insulator Cd 112.4 Private Issue B&e Vvnm / Mint Hemingray No. 62 Cable Antique Power Glass InsulatorLot Of 7 Vintage Glass Electric Power Insulators Hemingray See PhotosGreat Green Aqua Cd 132 Patent 1871 Bullet Style Glass Insulator2 Vtg Ef Johnson 62 Porcelain Ceramic Lighthouse Insulator Ham Radio ElectricalNice Light Green Cd 115 Mclaughlin InsulatorHemingray 60 Insulator With Very Nice TeethUnembossed Aqua Glass Spool Or Knob Insulator Cd 1087Fizzy Ice Aqua Cd 145 Petticoat Beehive InsulatorYellow Green Cd 162 Lynchburg No 36 Made In U.s.a. InsulatorCd 164 And Cd 102 Sterling InsulatorsWinged Chambers Attractive Resin InsulatorWestern Glass Manufacturing ( W. G. M. ) Co. Deep Purple Glass Insulator10 Vintage Collectible Wooden Telephone Glass Insulator Wood Mount Pegs Pin Pole