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]



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    

Pat.aug.3,1903 Twistlock No Tie Porcelain Insulator U-183 Unique ShapeBeautiful Dark Green Hgco Insulator!!! Beautiful Mint !!! Cobalt Blue Hemingray No.19 Insulator !!! White Swirls !!Threadless Glass InsulatorU-990 Antique Teapot Threadless Southern Porcelain Telegraph Insulator Civil WarCobalt Blue Hemingray No.19 Insulator *beautiful Coloring*Early Hemingray 1 Telegraph Telephone InsulatorInsulator Orange Amber Cd 162 (090) Rdp Close To Being Mint!!! Beautiful !!! Cobalt Blue Hemingray Petticoat Insulator Pat. May 2 1893 !!!Huge Aqua "mint" Two Piece Hemingray Muncie InsulatorBeautiful Vvnm Deep Reddish Orange Amber Cd 162 Hemingray 19 Signal Insulator!!! Beautiful !!! Honey Amber Hemingray No.19 Insulator !! See Other Listings !!Vintage B.g.m. Co. Lavender Purple InsulatorCrude C Mold Ec&m Insulator!!! Beautiful !!! Orange Root Beer Amber Hemingray No. 19 !!! Made In U.s.a. !!!!!! Beautiful !!! Hemingray No.19 7up Grn. !!! Mint !!! More Insulators In StoreMustard Cd102 Diamond InsulatorCd162 Hemingray Light 2-tone InsulatorPretty Nice Old Big Aqua Colored Hemingray Muncie InsulatorAwesome Amber "frog Eyes" Lowex Glass Power Insulator & She Ships FreeAntique " Sun Purple " Glass InsulatorPowerfully Nice Hemingray "mickey Mouse" Power Distribution Glass Insulator !!! Beautiful !!! Wfc Co.denver Colo. Petticoat !!! Purple !!! C Other ListingsAqua Egg Style Insulator!!! Beautiful !!! Red Amber Hemingray No. 19 !!! Please See My Other Listings !! Diamond Ice Green Glass InsulatorLot 6 Antique Glass Insulators Blue Green Telephone Electrical. Near PerfectVery Pretty Medium Purple Cd 145 Wgm Co Denver Beehive InsulatorSwirled Amber Hemingray 19 Signal InsulatorCivil War Era Telegraph Wire Insulator Dark Black Glass Threadless Rare !!! Beautiful !!! 2 Tone !!! Honey Amber Olive Hemingray No. 19 !!!Crazy Over Pour Cd 132 ( No Name ) Patent Dec. 19 1871 Green AquaPrimo! Purple Passion Glass Insulator Not Stained Or Dyed! She Ships Free!Whitall Tatum No. 1 Glass Insulator Light Bronze - Root Beer ColorAwesome Dark Yellow With Red Tiger Stripes Cd 152 Brookfield InsulatorAqua Cd 112 New Keg Insulator Hemingray Blue Muncie Type Glass Huge Two Piece InsulatorVictor U-860 Cobalt Blue Porcelain Insulator Marked For Private Power Line MintOrange Amber Cd 241 Hemingray-23 Made In U.s.a. Insulator Carnival 10-inch Corning Pyrex Sombrero Suspension Disk Insulator Three Different Knobby Dome Canadian Pony InsulatorHoney Amber Cd 162 Hemingray Made In U.s.a. No 19 Insulator Cd 133.4 [10] Patent Dec 19 1871 / H, Green Glass InsulatorMint Bluish W/bubbles Hemingray 60 Mickey Mouse InsulatorWe Mfg. Cd 126.4 Glass Insulator Excellent ConditionVintage Glass Insulators From Old Telephone Poles Lot Of 20 InsulatorsRarely For Sale Postal Tel Co. Telephone Glass InsulatorCd 143 Canadian Pacific. Ry. Co. Purple Insulator Old 6 Fin Amber Glass Electrical Insulator Railroad Telegraph 7" Tall Rare Vintage Pyrex Carnival Marigold Insulator By Corning Cd133.4 Pat Dec 1871 Insulator With Amber SwirlsInsulators Cd319 F.m. Locke Victor N.y. No 23 Insulator!! Beautiful !! Brookfield 55 Fulton !! Sage Grn. !! Pat. Feb.22&jan 1870 SwirlCd 133.4 Patent Dec. 19, 1871 Fat, Green Bullet Glass InsulatorEmerald Green Cd 102 Diamond Pony Insulator Glass Insulator Hemingray 60 Cd 257 Sdp Mickey MouseBeautiful Shiny! Carnival Glass Corning Pyrex Cd 235 Insulator Excellent! CleanWilkerson Glass Private Issue Electric Blue Miniature Boston Screw Top InsulatorA Great Hemingray Aqua Mickey Mouse Insulator12 Unused Wooden Insulator Pins