New to the hobby? Be sure to read Ted’s Top Ten Tips For New Insulator Collectors.
Want to know more about glass making? Read Frequently Asked Questions about Molding Glass Insulators.
Tip: You may also want to consult the Glossary of Insulator Terms.
If a picture is worth a thousand words, you should take a look at a few photographs of insulators in service!
The need for the insulator arose out of the discovery of electricity, which in turn led to the invention of the light bulb, telegraph, , and other electricity-oriented innovations. Also, as railroads began crisscrossing the continent, there came the need for signal devices. Electricity had to be moved economically from one place to another to meet the increasing demands generated by these new marvelous inventions.
According to Webster, to insulate means "to separate or cover with a nonconducting material in order to prevent the passage or leakage of electricity, heat, or sound." Communication and electric line wires in service must be kept as dry as possible in order to function efficiently, and to cut down on loss of current. The wires are kept off of the ground by being strung between poles. But something was needed to keep the wires and (sometimes wet) poles apart. This "something" had to meet three basic needs:
This "something" was the insulator. It was developed and improved upon over the years to meet those basic requirements and:
Often, one will have to consult the reference books to determine the CD number of an insulator. However, many newer insulators have a style number embossed on them, and one can look up that style number in this Manufacturer and Style Number to CD Number Chart.
Pintype insulators are grouped by a number of different characteristics:
There are also non-pintype insulators, which include spools, dead end insulators, and wire strain insulators.
Insulators were developed over the course of more than 100 years, for a variety of applications including telegraph, , and electric power distribution. Many shapes evolved to hold the line wire more efficiently or to increase the insulating ability. Larger insulators were developed to meet changing needs as larger heavier wires or higher and higher line voltages were used. In addition, some insulator shapes were designed for special applications. Many insulator companies would patent special shapes, designs or other attributes, even if in reality the invention proved impractical. Take a look at some of the varied shapes of insulators.
In general, insulators were not made in specific colors for any reason. The natural materials that were used to make glass, including sand and glass cullet, tended to make light aqua to aqua colored insulators. Some batches were more green, others more blue. In addition, some trace chemicals would alter the color of the insulators. Also, since all glass is produced using some glass cullet, the composition of the cullet would also have an impact on the color of the resultant insulator. Take a look at some of the varied colors of insulators.
Special colored glass insulators were produced in only a few cases. A Electric Appliance Company catalog gives this description:
Where several lines of different companies are on the same cross arm the lineman can distinguish his line by the color of the insulator. Different currents can also be designated by different colored insulators. We are prepared to furnish all styles of [Hemingray] insulators in red, blue, and amber glass, but shipments can be made direct from the factory only.
Add per M for colored glass . . . . . . . . . . . . . . . $8.00 net
It is interesting to speculate about what was meant by "red" colored insulators, given that "amber" colored insulator are also mentioned. "Blue" colored insulators probably refer to the bright Peacock Blue or the darker Cobalt Blue colors, and not what we call "Hemingray Blue" today.
In , prices ranged from $38.70 per 1,000 for No. 9 Pony Insulators (CD 106), to $154.00 per 1,000 for Cable Insulators (CD 257), to $1.00 each for a No. 0 Provo Type (CD 249).
There are many factors that determine an insulator's value. Shape, color, embossing, condition, desirability and rarity all affect its value. Most insulators are quite common and have little monetary value. The first step in determining your insulator's value is to determine which insulator you have. Even with a price guide in your hand, you have to determine which of the approximately 460 shapes, different embossings, and almost color combinations best describes your insulator. (And those numbers don't even include any foreign or porcelain insulators!) It is easy to list the common insulators, and also list the very rare insulators, but it is difficult to list all the thousands of collectable insulators that fall between those extremes! A slight difference in the shape of your insulator can affect its value by twenty fold or more. A slight difference in color can also significantly affect the value of your insulator. Unless your insulator is either very common, or very rare, it is best to consult a knowledgeable insulator collector or dealer; or to educate yourself and invest in one of the good insulator books available. If you are serious about collecting insulators, getting a good insulator reference book is a "must".
The two obvious ways to add insulators to your collection are either to find them, or to buy them. Finding insulators "in the wild" can be difficult, and if you find some, there is a good chance that they are common insulators. Most collectors buy (or trade) insulators. Many beginning collectors may find insulators at antique stores, flea markets, and the like, but you will soon realize that your section is very limited, and the insulators are generally overpriced. Although, there is a remote possibility of that rare bargain!
I believe the most effective method to add new insulators to your collection is to obtain them from other insulator collectors. A few years ago, I did an analysis of where we got our insulators from over the previous 6 years. I found about one third of them we bought from ads in insulator magazines, another third from writing for "for sale" lists also advertised in the insulator magazines, and the last third from insulator shows. Not much can top a good insulator show! You get to see a wide variety of shapes and colors, as well as prices! You also get to see exactly what you are buying. It is your opinion of the color, condition and other attributes of an insulator that matters. What better way than to hold it in your hand and look at it? Look at these show listings to see if there are any shows coming to your area. You might also want to check with your local insulator club for additional information. Insulator shows have one other thing going for them -- the people! The people are what make the hobby fun! Meeting collectors and dealers at shows is a great way to learn more and make new friends!
On the Internet, there are a number of insulators for sale pages posted, as well as the Insulator Finder! where you can register your wants and automatically be sent when insulators matching your wants are posted for sale!
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Last updated Sunday, August 31,
By Dario DiMare
OK folks, I’ll be honest—I don’t even know where to begin. Asking me to write an article on insulators is like asking a grandparent to write an article on their grandchild. A zillion pages later and I am still writing.
I will start off with just a little bit about me. I started collecting insulators in . I was actually digging for bottles in Ashtabula, Ohio, where I was born and raised, when I dug up an insulator with an date on it. Nobody knew what the date meant, but we knew the insulator was old. I was 10 years old at the time. I looked it up in the libraries but found nothing.
My first insulator, dug in Ashtabula, Ohio in . CD 131 Brookfield, Patent July 25, . See below to learn about CD numbers.
Six years later, I lied to my mother about sleeping over at my best friend’s house. With a new driver’s license in hand, I jumped in my $50 Pontiac Catalina and drove 400 miles to Washington, DC, to look up the patent at the Library of Congress in the National Archives. Gas was about 50 cents a gallon, and I had one loaf of bread, one jar of peanut butter, a moving blanket, and a half-gallon bottle of water (which was glass back then). So, by stealing the peanut butter and bread from mom, filling the water up in the gas station bathrooms, and sleeping in the back seat of the car, the total round trip to DC and back cost about $30. It took a lot of Dr. Kilmer’s and blob top soda bottles sold to the antique shops to get the $30. The July 25th, date was the patent for screw threads in insulators. I still have the insulator.
Goto ZheXi to know more.
Now having owned as many as 12,000, and having handled more than ten times that amount, with thousands of hours spent hunting and researching, I feel comfortable writing a little about insulators.
Here is some fundamental information about insulators.
Insulators are non-electrical conducting objects, usually made of glass or porcelain, intended to insulate the current running in a wire from grounding out, especially in fog or rain. Most often they are mounted on wooden pins on the cross arms of poles. If they insulate properly, the electric signal or current will meet its final destination in a safe and useful manner.
Most insulators in the U.S. were made of glass or porcelain. There are some composite, gutta-percha, rubber, and even wooden insulators. I will be speaking primarily about glass insulators since they are my specialty (with the exception of very early telegraph insulators which were made of various materials including porcelain).
Materials: Telegraph insulators made out of glass, gutta percha, composition, wood, metal, and one of the earliest plastics ever made.
Ramshorns: Very early ramshorn type insulators. The ramshorn itself is iron. They are set in glass, gutta percha, rubber, and composition.
Porcelain threadless: A very rare and diverse collection of threadless insulators made out of porcelain.
Glass insulators emerged in s America with the invention of the telegraph. The early telegraph insulators were mostly threadless, pin-type insulators. There were some glass blocks and ram’s horn types as well. The very first glass insulator, the bureau knob, was used by Samuel F. B. Morse on the line from Baltimore to Washington. The first electronic telegraph message in May of stated “What hath God wrought?”
Left: This is the first glass pin-type insulator first used in the s. CD 780, Bureau Knob. Right: The 780 and the glass blocks were the first insulators used on the telegraph and date back to the s. CD 780 and CD glass blocks.
The threadless insulators are kind of like pontil bottles, with a similar end date of about to when my buddy Louis A. Cauvet patented the threaded insulator. The threadless were also primarily used on telegraph lines, since the was not invented until , when Alexander Graham Bell said to his assistant, “Mr. Watson—come here—I want to see you.”
Threaded insulators were then made by the millions and used throughout the world. Many of the glass houses that made bottles made insulators as well. The last glass insulators were made by Kerr in the early s. Yup, the same guys that made the fruit jars.
Left: This is a pair of transition insulators. Like with some bottles, there are both pontil and non-pontil bottles using an identical mold. These insulators have the same outer mold and only the plunger forming the threadless or threaded pin hole are different. CD 736 threadless and CD 135.5 threaded E.R.W.’S. Right: This is the last glass insulator ever made. How depressing! Waaaaaah! CD 155 Kerr.
Put very simply, insulators are made in every color that bottles, china, and windows were made in. Back then, in almost all cases, the color did not matter. A lot of insulators were made from “end of the day” glass; instead of throwing out the batch of glass at the end of the day, glass makers would fill up insulator molds and sell them by the hundreds. Appearance was not a big deal with insulators. I have a few “crystal” insulators made in Sandwich, Massachusetts. Imagine turning one of these babies up-side-down and drinking champagne out of them so you could fit in with the bigwigs?
The shelf above has the complete rainbow of color on it: red, orange, yellow, green, blue, and purple. Like bottles, aqua is the most common color, but some of the rarest insulators are aqua. A few insulators were factory-coated with carnival glass or a flashed amber. The most sought after colors are cobalt blue, yellow, 7-Up green, and purple. Some of the purple insulators were originally made clear, but due to the sun’s effect on the manganese in the glass, they actually turned purple.
Like with bottles, there are many factors that make an insulator “good” or more desirable. Here are a few of the factors:
Condition is a big deal with most insulators. There are fewer mint condition insulators than bottles, due mostly to the industrial use. Rare insulators in mint condition command a premium.
Color is very important. A $10 insulator commonly found in aqua can fetch you $10,000 in a rare color. And there are a few cases like in the CD 701.6 where the aqua insulator is worth five times more than the dark green CD 701.6.
I just had to put this in. The manufacturer of this CD 121 is R. Good Jr. out of Denver, Colorado. Pretty hard to argue about this being a “good” insulator. Ha! CD 121 Good.
Age also adds value. Most threadless insulators are worth more than threaded insulators. However, the ten most valuable insulators in the hobby are threaded. I am not being a wise guy, just being honest.
Embossing is also a major factor. Having just common embossing can add value. Having a rare embossing can add even more value. The CD 150 Brookfield books for about $500, and the CD 150 Barclay books for $5,000!
Rarity obviously adds value. I know of some CDs where I am almost certain that fewer than a dozen exist. They may have made hundreds or thousands, but to my knowledge, very few have survived, and the ones that have are very difficult to find.
Desirability is the big wild card. Some insulators are just more desirable than others. This makes no sense when you look at statistics, numbers, color, or age. Some are just flat out more desirable. I know of about five or ten CD 100.2s and CD 100.6s. They are extremely rare, and yet the CD 141.9, of which I know of about 20 or 25, still fetches two or three times more on the market.
The 100.2 is extremely rare and books for several thousand dollars. The 141.9 is not nearly as rare and books for three or four times more than the 100.2. (Please be careful if buying a CD 100.2. The CD 100 is very similar looking, and the CD 100 is very, very common, and valued at one dollar or less.) CD 100.2 Surge and CD 141.9 Emminger’s.
CD stands for Consolidated Design and is the numerical designation used to identify glass insulators. U numbers are used for porcelain, and M numbers are used for multi-part porcelain insulators. N. R. “Woody” Woodward invented the CD system in the early s. He was an early collector and researcher, solely responsible for categorizing all of the glass insulators in North America. He partnered with Marilyn Albers to assign CD numbers to the foreign glass insulators. There is some logic to the numbering system with simple pin type insulators starting at CD 100 and ending at CD 350; the threadless claiming the CD 700s; and some of the block types and more unusual shapes reaching the s. When listing an insulator for sale we usually state it as CD#, name, color, condition, and price.
For example: CD 731, Tillotson, aqua with bubbles, mint $0.00
I was asked by N. R. Woodward to take over the CD assignments for the insulator hobby, so now I am responsible for assigning any new CD. We have the National Insulator Association (NIA) at www.nia.org as our national association and Insulator Collectors On the Net ICON at www.insulators.info as a great collectors chat and web site.
This is my favorite insulator which I dug up in New York in . Great condition and 1,444,444 seed bubbles, which I counted all by myself. CD 731 Tillotson.
If you have any questions about insulators, please feel free to contact me. Let me know your time limit, because I can ramble on forever about these stupid things. Happy collecting!
You can reach Dario by mail at Dario DiMare, 318 Main Street, Northborough MA . Give him a call with your insulator questions at (617) 306-. And, send your insulator mysteries and photos to .
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