Vintage ceramic electrical insulators

Vintage ceramic electrical insulators DEFAULT

antique porcelain electrical insulators

$$/ Piece

Pieces(Min. Order)

Pin Porcelain Insulator(ANSI) •Material: Porcelain •standard: ANSI •ANSI class: //// •characteristics is following table: Cat/NO A A A A A ClassANSI Creepage distance (mm) Dry arcing distance(mm) 57 86 Cantilever strength(kn) 13 11 11 13 13 Low-frequency dry flashover (kv) 35 45 56 65 80 Low frequency wet flashover(kv) 20 25 30 35 45 Critical impulse flashover ,Pos(kv) 50 70 90 Critical impulse flashover ,Neg(kv) 70 85 Power-frequency puncture voltage(kv 50 70 90 95 Test voltage to ground(kv) 5 5 10 10 15 Maximum RIV at KHz(uV) 50 50 50 50 Net weight ,approx. (kg) 1 Number in standard package 60 40 30 16 1

Sours: //


Welcome to the Porcelain Insulator Collector's World of Mud!


Porcelain Overview

Similar to their glass counterparts, porcelain insulators date back to before the Civil War for telegraph wires.  In North America glass was always the predominate material for communications insulators but porcelain has become the standard for power distribution due to its greater strength and surface resistance.

Porcelain insulators did receive the same level of interest as glass in the early years of insulator collecting, but have been gaining popularity in the last ten years.  They are equally historically significant as their glass counterparts and available in as many colors and significantly more styles. Within the last 10 years or so a number of factors have contributed to the rapid increase in interest in porcelain:

  • More information has surfaced about the porcelain insulator business and a number of dedicated individuals have written books, articles, and reprinted catalogs that have significantly increased collector knowledge and interest in the porcelain side of the hobby.
  • Glass prices have been on the increase in recent years, making porcelain an attractive and affordable alternative.  Porcelain insulators are now much more available at insulator shows.
  • More and more early "classic" porcelain has been taken out of service as utilities increase distribution voltages and collectors go "mud hunting"
  • Collectors have realized that the amount of color available in porcelain is very significant and has increased as more distribution lines are dismantled.
  • The increase of information available on the internet as well as the variety of porcelain insulators available on Ebay give a larger population exposure to porcelain insulator collecting.
  • More historical interest has been generated in the early development of power generation and distribution which has been primarily dependent on porcelain insulators.  Current linemen are much more familiar with porcelain, as very little glass remains in use today.
  • New styles are still being found every year (if not every month!)
  • Old trade journals have increased collector knowledge of where to find the early classics.

I hope you've enjoyed this overview of porcelain insulator collecting. We look forward to meeting another "Mud Hound" on-line!!!

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Please send your questions and comments to Bob Berry at

Last updated Sunday, August 31,

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Markings Found on Porcelain Pin-Type Insulators

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The list below shows the text version of various markings found on porcelain pin-type insulators.  For markings on cleats, knobs, standard porcelain, and  wall tubes, please those listings using the links at R=&#; Homeunder the subject "Other Insulators".  Details and illustrations of each marking will be added at a later date.


Not all combinations of markings were shown in the Value Guide, which was not intended to be a complete listing of marking types.  All markings are incuse unless otherwise indicated.  Marking methods on multipart porcelain insulators are too numerous to even discuss or keep records on, so most of the markings shown in multipart section of the Value Guide are either typical, unusual, or rare markings used on very old specimens.

Incuse:  "Incuse" markings result from striking the leather-hard clay with a marking stamp which produces letters and/or designs cut into the surface.

Embossed: Very few porcelain insulators have the raised markings known as "embossed" markings.  They typically are found on dry process insulators.  The major exception is the "embossed" Ohio Brass trademark on the crown of their wet process insulators made from to about   Most collectors use the term "embossed" when describing markings on porcelain insulators.  This is a holdover from collecting glass insulators were nearly all markings are raised above the surface.  Unfortunately, the use of "embossed" is so ingrained in our hobby that it is impossible to get people to change.  Fortunately, few porcelain insulator styles (U-numbers) have both dry process specimens with an "embossed" marking and wet process specimens with one of the other marking types.  The only embossed marking on multipart porcelain insulators is the typical (but much larger) "O-B" used by Ohio Brass on its unipart styles.  It is wrong to describe "incuse", "u-g", "r&#;e", or "s-b" markings as "embossed", and it leads to confusion for many serious collectors.

Recess-embossed (r-e): This is a pseudo-embossed marking obtained on wet process insulators by striking the damp clay body with a device that leaves raised letters on a recessed background.

Under-glaze Ink (u-g): This marking was obtained by using a rubber ink stamp to apply the ink mark on the dried insulator clay body before the glaze was applied.  The ink would soak into the surface of the dried clay.  The first use of this type of marking was on insulators made for Fred Locke by Electric Porcelain & Mfg. Co. from to and later at his factory in Victor, NY.  Ink colors of black, blue, and green were used by that company.  The use of the under-glaze ink marking was revived several decades later and can be found on modern specimens from several different manufacturers.

Over-glaze Ink(o-g):  This marking was applied by using a rubber ink stamp to apply the mark on top of the dried glaze before the glaze was fired.  A colored glaze was used to make to make the marking.  Thomas is known to have applied this type of mark using using an orange glaze for certain QT multipart styles (example: M with o-g marking THOMAS / QT).

Sand-blast (s-b):  Very few sand blast markings were indicated in the Value Guide because many collectors did not note marking types and there were few reports of "s-b" markings from those that did.  This marking is applied by holding the finished insulator against the contoured head of a sandblast machine.  This marking method was never widely used on uniparts.  The only unipart insulators ever marked by sand blast were the Line Material and McGraw-Edison units made in the 's and 's at the Macomb, IL plant, and one used in 's by Ohio Brass on larger insulators.


Companies and Markings   For more information on companies, go to the Companies list.


Akron High-Pontential Porcelain Co.:  pin-type insulators ; taken over by Ohio Brass in

American Electric Co. Inc.:  Manufacturers of electrical supplies; sold U circa

Automatic Electric Co. Inc.:  Manufacturers of electrical supplies; sold original U insulator circa

B in a circle: Found under top skirt of M  These insulators were made in Europe (Italy?) and used on lines in British Columbia.  Don't confuse this rare marking with the relative common Ohio Brass markings, which is a B inside an Oval.

Brown, Boveri & Co. ()

Bennington Potteries (threadless styles circa 's)

B & O: Baltimore & Ohio Railroad

C.C.V.F.:  Unknown meaning on insulators found in Florida.

Cent mark

Central:  Unknown meaning on certain Thomas insulators.



C. F. Co.  (unattributed)

A. B. Chance Co. () 

C.N.R.:  Canadian Northern Railway

Cook Porcelain Insulator Corp. (circa early 's to circa )

Cooke Wilson E. S. Co.:  Jobber of electrical supplies.  Dry process mine insulators with this marking, U, were possibly made by American Porcelain Co. ().

Cooper Power Systems  The "" may be a catalog number.  The "" is the ANSI style.


C.P.R.:  Canadian Pacific Railway Co.

C. P. R.  


CTS and CTS Made in Canada:  Chicago Telephone Supply Co.

Delta-Star Electric Co.: H. K. Porter Co. purchased the old Thomas plant in Lisbon, OH ()

Electric Porcelain & Mfg. Co.:  Their insulators have an under-glaze ink marking with Fred Locke's name and patents.  They made insulators for him from late until about   For Fred Locke markings, click on this link: Markings

Federal Porcelain Co. ()

Findlay Electrical Porcelain Co.()

Franklin Porcelain Co.  (circa early 's to circa )

Fred Locke: Locke Insulator Mfg. Co. prior to   He began buying porcelain insulators in from Thomas, in from Imperial, and in from E. P. & M. Co.  He began making is own porcelain insulators in until his retirement in Dec.   For Fred Locke markings, click on this link: Markings

G:  Unknown meaning.  Insulators may have been made by Illinois Electric Porcelain Co.

General Electric Co.(U, U, and UA made circa )  Markings below were used when GE had ownership of the old Locke factory in Victor, NY.

GK:  Unknown meaning.

Gladding Ceramic Insulator Co. Inc. (circa 's)

GLEN:  Glen Electric Co. (circa )

Gould Inc.:  Gould, Inc. ()

General Porcelain Co. ()

G. T. P.:  Grand Trunk Pacific Telegraph Co. (Canadian)

Harloe's Patent: U

Hartford Faience Co. ()

I.E.P.:  Marking used by Illinois McGraw Electric Porcelain Co. () and after a merger changed the name to Illinois Edison Co. ().

Illinois Electric Porcelain Co. ()

Imperial Porcelain Works (pin-type insulators: )

I-T-E Imperial Corp.() 


Jeffery-Dewitt Insulator Co. ()

Johns-Manville:  Jobber of electrical supplies.

Knox Porcelain Corp. ()

Lapp Insulator Co. (circa 's)

Lima Insulator Co.  ()

            Lima 32     Lima 36

Line Material Co. ()

Locke Insulator Mfg. Co. (); Locke Insulator Corp. (); and Locke, Inc. (pin-types: )

Various incuse markings:

.LOCKE.    LOOKE    LOCRE    77    


Locke R=&#; (see Locke):  Marking (shown inside outline of an insulator) used by Locke Insulator Mfg. Co. ().


Macomb:  Marking on dry process insulators made by Illinois Electric Porcelain Co. ()

Macy Insulator Macy Ind:  Unknown meaning on U insulators found near Macy, IN.

McGraw Edison Co.  ( present; purchased by Cooper Power Systems in which still uses a different u-g ink ME marking.)

Mershon Type:  Ralph Mershon patent No. , dated June 7,   The marking is found on U made by R. Thomas & Sons Co.

M & H:  Manwaring-Hessel patent on UA.

MP:  Missouri Pacific Railroad or Missouri Pacific Telegraph Co.

N.A.T.CO.:  North American Telegraph Co.

N.E.P.:  Maybe New England Power Co.

New Lexington High Voltage Porcelain Co. ()

NGK:  NGK-Locke (circa 's)

Ohio Brass Co. (marked own production: circa 's) 





O. P. Co.:  Ohio Porcelain Co. (circa )

Pass & Seymour Inc. (pin-types: circa )

P & S  


Peirce Patent: U

Peru Electric Mfg. Co. (only known pin-type style, UB: circa )


embossed or incuse

Pierce Patent: U

Pinco:  Porcelain Insulator Corp. (; last two years marking used by Industrial Ceramics)


Pittsburg High Voltage Co. ()

Porcelain Products Co. (present; no distinction was made for this later company in the Value Guide listing.  All insulators for the older and newer companies are shown as P. P. Inc.)

Porcelain Products Inc. (; see P. P. Co. above)  

POSTAL:  Postal Telegraph Co.

P.R.R.:  Pennsylvania Railroad    

Purkey Patent: U

Ranson Patent: U

Slusser Patent: U

SOO:  Soo Line Railroad

Square D Co.  ()

R. Thomas & Sons Co. (pin-types: circa )


R. Thomas & Sons Co. (Odd markings)


B    B    B    B    

Triangle M:  Marking (M inside a triangle) used on insulators made by Illinois Electric Porcelain Co. from

Victor:  Marking used by Fred Locke () and Locke Insulator Mfg. Co. ().



Victor Insulators Inc.  ( and present)


Victor R=&#; (see Locke):  Marking (shown inside outline of an insulator) used by Locke Insulator Mfg. Co. ().  The larger size insulator logo marking was used first.  The smaller size insulator logo marking replaced the larger logo marking sometime in the late 's. 


Westinghouse Electric Corp. ()



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Stats Of Hits


Antique glass insulators are a low cost but very popular collectible that come in a myriad of fun shapes and colors. They're easy to find, and make a colorful, decorative display in your home, office, or business.

History of Glass Insulators

The first insulators had nothing to do with telegraph wires or electrical wiring and were used to protect homes against lightning strikes. However, these small glass cups were a vital element in the development of massive communication technologies as they helped telegraph and telephone wires keep their electrical currents from losing strength during their transmissions. This consistent flow of electrical energy allowed for speedy connections that simultaneously connected people around the world.

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Industrialization and Glass Insulators

Glass insulators for wiring began to be manufactured in the midth century in response to the needs born out of the technological advancements being made during the period. Samuel Morse had successfully used the first telegraph machine in , and by telegraph lines were being strung from one coast of America to the other. Thus, the need for insulator technologies arrived.

As these communication technologies developed, with more complex wiring systems and larger amounts of electricity being fed through lines positioned close to people's homes, the historic glass insulator was retrofitted to be able to be used in conjunction with telephone and electrical wires. The first insulators of this type were small because they only needed space for one wire, but as time went on, the insulators became larger and reflected the growth in demand and power of these communication systems.

Rural Electrification Act

In , President Roosevelt and Congress passed the Rural Electrification Act, which provided funding for rural areas to gain access to electricity and telephone systems through a public works project that sought to install electrical wires throughout the electrically free region. This surge in the number of electrical systems around the United States increased the need for the glass insulator and more companies specializing in manufacturing them sprang up as a response.

These glass insulators reached their peak use between By the end of the s, electrical companies had begun transitioning to porcelain insulators - a transition which was complete by the end of the s. This meant that most of the insulators which collectors hunt down today come from the earlyth century. In terms of modern telecommunications, most electrical systems use cable, which doesn't need insulators at all, meaning that there's less of a need for these insulation technologies. Similarly, those that still require insulation utilize porcelain instead of glass as it's cheaper to manufacture.

Insulator Manufacturing Companies

There were hundreds of companies that manufactured these old insulators. In fact, glass companies like Indiana Glass manufactured insulators at the same time that they produced their highly popular Depression glass lines. Some of the manufacturers who produced antique glass insulators are:

  • Hemingray
  • Indiana Glass
  • Kerr Glass Manufacturing
  • Louisville Glass Works
  • McKee and Company
  • National Insulator Company
  • Owens-Illinois Glass
  • Pacific Glass Works
  • Star Glass Works
  • Whitall Tatum Company

Colors of Antique and Vintage Glass Insulators

As with most competitive industries, all of these companies produced insulators which had a slightly different design or color. The most common colors of insulators were clear and aqua; however, there were other colors and these ones can be quite rare and valuable. Some of the colors were:

  • Amber
  • Cobalt blue
  • Green
  • Two tone
  • Yellow green
  • Olive
  • Light blue
  • Purple

Old Insulators Made From a Variety of Glass Sources

Since the manufacturing companies didn't solely make insulators, they often used leftover glass from other projects to press a few insulators. Because of this, you may occasionally see an insulator in opalescent glass, vaseline glass, slag glass, or another unusual color (or even mixture of colors). These insulators are very collectible because of how rare they are. Other manufacturers recycled old bottles and other glass items, which resulted in swirls of color, bubbles, and other interesting effects in the insulator. According to a Collector's Weeklyinterview with insulator collector Ian Macky, cobalt blue is the most popular color among collectors.

Beware Color Manipulated Insulators

Keep in mind that unethical sellers can alter the color of an insulator by applying heat or radiation and later claim that it's a rare antique and charge much more. It's difficult for even experienced collectors to discern the differences in natural and color manipulated glass insulators; so, it's best to be on guard against anything that doesn't seem right. If you are considering the purchase of an expensive insulator, it may be a good idea to have an experienced collector take a look and give an opinion on its value before committing to a purchase.

Glass Insulator Values

Old glass insulators can range in value from $2 up to over $, depending on many different factors. Like other antiques, glass insulators are evaluated on several criteria, including:


Glass blowing technology rapidly shifted alongside communication technologies' advancements, meaning that a great way for you to parse out a glass insulator's age is by looking at the glass itself. If you can't make out the CD numbers, then finding bubbling and a roughness to the glass can be indicative of an early molding, whereas completely transparent pieces likely came from the mid-century.


Generally, color is the predominate factor that determines if a glass insulator is rare or not. The most common glass insulators were light blue and/or clear, with unique colors like rich purples and greens, bringing higher values at auction.


The most common glass insulator was made out of the 'beehive' shape, but finding insulators of different shapes can be a lucrative advantage.


Insulators without any signs of cracking, melting, or staining will fetch the highest values at market, while those with obvious signs of wear and tear are going to have affected values.


Ultimately, with any antique or vintage collectible, you're at the market's mercy. Whoever is currently collecting and what their interests are is going to have a significant impact on how much your items are going to sell for.


As with most antiques, the manufacturer can increase and decrease an item's value. Some collectors are willing to pay more just for an item based on who made it, and the same can be said for glass insulators. Similarly, having markings from less-common manufacturers can make insulators more valuable thanks to their rarity.

If you're thinking about buying or selling some old glass insulators, you're probably going to be looking at spending/receiving about $20 per insulator, give or take. On average, these glass insulators tend to sell for around $20, though there are special instances where insulators can sell for significantly more than that. Generally, the insulators that sell for more are rare, either because of their manufacturer or their color. For instance, this purple Canadian insulator sold for just over $85 and this unusual Merhson power glass insulator from the lateth century sold for almost $

Electrify Your Decor With Antique Glass Insulators

Collecting and displaying antique glass insulators can be a low cost, enjoyable hobby. Electrify your decor with an antique glass insulator as these colorful bits of history can create a cheerful bolt of color and charm to any nook in your home.

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Ceramic electrical insulators vintage

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Porcelain insulator collection

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