Collecting any vintage item is a matter of balancing investment with possible returns and personal enjoyment—vintage glass insulators are exactly the same. Thankfully, starting or expanding an insulator collection doesn’t have to be financially straining … unless you want to make that investment.
Vintage glass insulators can be worth anywhere from a couple of bucks to thousands of dollars. The most common insulators can be obtained from antique stores, online or brick-and-mortar, for under $15. More unique models— whether by color, style, or manufacturer—can be acquired for around $60 to $250. The rarest pieces though can range up to a value of $8,000.
Read on for a break-down of what influences vintage glass insulators’ values, some nuances to take into consideration, and a look at the top five highest-valued insulators.
What makes an insulator valuable?
There are seven aspects to consider when establishing the value of a vintage glass insulator, each with their own specifications, here’s a detailed look at each.
The majority of insulators that were made were also used—it’s rarer to find mint lots of insulators than bottles, for instance. There have been a few here and there: an unopened crate in an old factory, a collection of barrels, etc. As such, insulator condition is a prime aspect of value. Cracks, chips, and scuffs all impact the insulator’s worth, with two interesting caveats.
The first is that the impact of condition on price often falls away as the rarity of the piece increases, so if the insulator is an unusual CD (Consolidated Design, see Shape) or color, the price can be less impacted.
The second is by the sheer nature of intended purpose, used insulators are usually recovered in a filthy state, covered by years of soot, railway fumes, and outdoor grime. Unlike some other antiques—like silver, where the patina can be a positive part of value—railway soot is not a popular thing to have around as it inhibits seeing the insulators’ original color & shape. Cleanliness, thus, is an impactful part of condition; a clean insulator will be more attractive to buyers.
Color is one of the biggest influences on value. Aqua and clear glass were the most prevalently used for molding insulators, but anything from milk glass to cranberry glass to clear with internal swirls of color is possible. Some insulators were coated with iridescent surfaces as well. Manufacturers often threw the glass remaining at day’s end into insulator molds instead of wasting the excess. This meant that insulators were made in a wide variety of glass, sometimes even mixed within one insulator. Of note here is that violet glass may not be the original color of such insulators (see below) and there were simply no originally deep red glass insulators made.
As is norm with antiques and vintages, the older an insulator is, the more rare and therefore valuable it is often considered. Of course, that statement is balanced by how many of the particular insulator in question were made; sometimes that gets as detailed as how many were made in a particular year, as with Hemingray dating their models. Check out our full article on identifying the age of your insulator here.
Embossing started later than making insulators, many of the earliest are a challenge to connect to their manufacture because there’s no embossing included. But by the 1870s, companies had begun noting their name and/or the model of the insulator via embossing, generally on the exterior surface. Hemingray had a particularly detailed approach to embossing that renders their insulators identifiable in company, mold number, and year made, using only a few numbers and a series of dots.
Insulator shapes are defined by CDs, or Consolidated Design Numbers. A system organized by N. R. Woodward in the 1950s, the intent of the CDs is to classify pin-type insulators by design features, regardless of mold number, manufacturer, or color. Details like how many grooves on the exterior surface, how many inner skirts, and whether the base is flat, rounded, or has drip points all impact what number an insulator is assigned to. Some CDs have hundreds of existent pieces, while others have only a handful … or even one known. CDs start at 100 and continue into the 1000s, as follows:
CD-100 through CD-375: North American threaded
CD-376 through CD-699: foreign threaded
CD-700 through CD-799: North American threadless (these will be largely pre-1865)
CD-800 and up: block and other non-pin type
Some companies, like Brookfield, Corning, & especially Hemingray, produced millions or even billions of insulators, while others produced only a few hundred. (Hemingray produced their billionth insulator in 1937.) If the manufacturer is identifiable, usually either by an embossing or because they only ever made a particular model, then that may influence the price based on manufacturer rarity presently.
For instance, there is only one CD-162 insulator model with the Hamilton Glass Works & Company embossing on it. The CD-162 style is a common, widely produced insulator—Hemingray produced four variants over the years, while Brookfield had five. But one with this particular embossing on it would likely be more valuable than others. Check out our full article on when and where vintage glass insulators were used for more information.
That brings us to the final aspect, that of desirability. The challenging, constantly-fluxing part of nearly any marketplace—where something in high demand one year may not fetch the same price the next. There are several reference books that can help establish a starting point for value, but ultimately market research is a necessity when you go to buy or sell a vintage glass insulator.
Are clear glass insulators worth anything?
Clear glass is a complicated question that requires a touch of back history. Glass, based on the core ingredients used to make it, is naturally a light aqua blue. Prior to the 1930s, clear glass was most commonly created by using either manganese or selenium oxide as a neutralizer. After this time, arsenic became more commonly used.
Manganese and selenium oxide both oxidize when exposed to ultraviolet rays; in much the same way as copper turns green, clear glass with these minerals turns to a shade of lavender or amber over time. Lead-neutralized glass, on the other hand, does not.
The result is that clear glass insulators are both inexpensive and highly valuable. If the piece happens to be a genuine pre-1930 insulator that retains its clarity (most likely a mint-condition warehouse find), it will be highly valued. Otherwise, clear glass insulators are likely later mass-produced items that aren’t as valuable for being a common color and more recently made.
Which glass insulators are the most valuable?
Color is the most obvious aspect of an insulator collection and the widest ranging difference. Because of this, rare colors are often the most valuable insulators. Railroad signal insulators, which were purposefully made in multiple colors to differentiate different circuits, & end-of-day presses are where a lot of the interesting colors come from.
Of course, rare CDs also hold their own, going to show that above all, rarity in some way is the influencing factor. Cobalt blue is an interesting exception: because it’s such a deep, wonderful color it is extremely popular to collectors despite not being that uncommon, with thousands of insulators made in this hue.
What glass insulators are worth the most money?
The most common insulators can be bought for only a few dollars, with eye-catching and unique specimens available for under $100. But these are the top five most expensive insulators: impactful combinations of beauty, age, and rarity coming together for some truly astounding prices.
- CD-130.1 Cal Elec Works: $5000-8000
Charming in cobalt blue, these were made for the first long-distance telephone line, established in California in the 1870s by a mining company. The shape is unusual, with three protruding wire holders instead of the typical channels.
- CD-141 Twiggs: $3000-4000
At 4’ tall, this is a rather large insulator. There are only thirteen known models of this type, made in 1905. As with the previous design, this one does not feature the usual skirt channeling, rather securing the wire between two balls at the top of the insulator.
- EC&M: $2500
This manufacture’s insulators were used for telephone lines ran by mining companies in the 1870s again, from California, through Nevada, Arizona, & Utah—even as far north as British Columbia.
- 1903 Gregory: $1500-2500
Gregory insulators, made in 1903, were used along railways in the Sierra Nevada Mountain area of California. They came in the typical aqua green with a wire channel.
- Montreal Telegraph Co.: $1100
Among the earliest communications companies in Canada, Montreal Telegraph Co. was founded in 1847. Their insulators were all light blue until the 1880s, these early ones are rare to find on the market now but if you get the chance, look closely. You’ll see a light milky effect in the glass, adding to the physical beauty of this design.
These are “firsts” of insulators, catching their high places in the market by being limited commodities from relatively early projects. Most insulators are far more financially approachable. Take the Hemingray-42 for instance: a quick search on Etsy will give you innumerable options, around $15-22, for this lovely and classic piece of insulator history.
Armed with insight on how to determine value for vintage glass insulators … happy hunting!