Collecting Glass Electrical Insulators


Glass electrical insulators were once familiar sights along railways and their rights-of-way; today, however, collectors treasure them for their beauty and economic value. The Amazing fact about commercial glazing relacement.

These colorful glass discs were attached to wooden pegs at the cross arms of telephone and telegraph poles with wooden screws, creating an insulator that protected against electricity jumping too far between poles and arcing between them. Their wider bottom “skirts” prevented this occurrence.


Glass electrical insulators were first invented in the 19th century as technological innovations increased demand. Samuel Morse had his telegraph lines strung alongside railroad tracks across America, which required them to have protective insulation against shorting out. Insulators provided such protection.

People interested in glass insulators tend to collect them for upcycling or decorative use in their homes or for display as decorative items. Insulators make great candle holders or flower containers when placed strategically around the room, and their aesthetic beauty makes them quite charming when in a strategic spot. Due to their porous surface, insulators collect dirt and dust to maintain them without damage or wear. A collector should clean each insulator regularly using mild dishwashing liquid and warm water, which will typically remove any accumulation.

An insulator’s value will depend on its style and condition; this is particularly true of those manufactured by popular manufacturers from years gone by. Such insulators usually bear their manufacturer’s name, such as Merhson power glass insulators having greater worth than generic versions from less renowned makers.

Age can also play a factor in an insulator’s value; pieces produced during the mid-1850s to early 1860s cost more because they are rarer and in better shape; threadless insulators from this era are highly sought-after by collectors.

Collectors must understand their collection’s various kinds of glass insulators to appraise them appropriately. Insulators are generally organized using CD numbering – created by early collector and researcher N. R. “Woody” Woodward as a classification system that groups them by shape and profile rather than exact markings or glass colors used for production.

Insulators come in various categories beyond just pin-type communications and electric power line insulators; these may include lightning rod insulators, radio wire “strain” or “egg” insulators, inside-home wiring knob insulators, and battery rests. Furthermore, there are various colors of insulators, such as amber, cobalt blue, light blue, and green.


Glass insulators come in every hue imaginable, from rainbow hues to shades of blue, green, and amber. Collectors often seek out rarer hues like purple or amethyst, which require special care in production; others like clear green and light cornflower blue are still highly prized by collectors of glass insulators.

Before glass insulators became widespread, they were typically made out of wood and metal. To protect people and animals from being hit by sharp metal stakes, wooden poles were often topped with glass insulators as a preventive measure, and this served to both insulate electricity and keep people away.

These glass insulators were practical household items, so their manufacture often fell to the same companies who produced art glass or other household items. Glass insulators were widely used by the telegraph, electric power, and telephone industries.

Some insulators were manufactured in all rainbow colors, while most were limited to just a few shades. Aqua and clear were two popular choices due to the companies already producing art glass or canning jars in these hues. Insulators also came in other hues to distinguish one utility company’s lines on one pole from another.

Colored green wire insulation was often designed in various shades to distinguish its wires from each other and aid companies in keeping track of what was on a pole and quickly identifying damaged insulators. Different colors designed to serve this function included a signal or flashing red to warn people of dangerous situations on the line.

Glass insulators were often identified by CD numbering, popularized by N.R. “Woody” Woodward as a collector and author. This identification method involves categorizing shapes by profile and color to assign CD numbers; more distinct colors or shapes were given higher than usual. Today’s electrical systems rarely require insulation, so glass insulators have become less necessary than they once were during the early 20th century.


Many people collect glass insulators for the aesthetic value they add to any room in the home, while others collect specific types of them for historical significance. Most antique glass insulators can be found for under one dollar, while some of the rarest was once used to connect telegraph and telephone systems and can fetch several thousand dollars or even more depending on color, shape, and manufacturer. Insulator prices can often depend on these elements alone.

Not only can an insulator’s color indicate its value, but the markings and base type also have much to do with its appeal. Insulators with raised markings on smooth bases are generally considered more desirable than those featuring sharp drip points or drip point insulators with strong drip points. Collectors frequently refer to CD numbers when identifying an insulator; however, many collectors also pay close attention to other details that help determine its worth.

Manufacturer reputation can play an integral part in setting the price of glass insulators, with prominent names such as Merhson power insulators or purple Canadian insulators commanding higher valuations than lesser-known firms. Threadless styles from the 1850s or 1860s cost more than those from prolific production areas such as Minnesota or Wisconsin.

Insulator collectors tend to specialize in one particular glass company, style, or color of insulators. Over time, they become experts in their specific field, researching its history, which types were manufactured at what time, and any embossed markings that may exist on an insulator.

Damaged glass insulators can have significant depreciating value for collectors. Most collectors are exceptionally particular about this due to mass production with poor quality control prevalent during their show; one crack or chip in an insulator will render it worthless in most instances.

Glass insulators were at their most widely used point during the early 20th century. After this, electrical and telecommunications systems transitioned from them due to being cheaper to manufacture; nevertheless, those still available today remain valuable collectibles and fetch some good cash for their owners.


Glass electrical insulators make an excellent collectible and can even be quite valuable, with collectors willing to spend hundreds on rare or unique insulators in good condition and with distinctive markings, colors, and manufacturers. The value of such items largely depends on the situation, markings, color choice, and manufacturer.

Insulators in excellent to-mint condition command much greater prices than those showing signs of use or age. Damage to an insulator’s wire ridge or other non-visible areas will significantly diminish its value.

One way of assessing an insulator’s value is by searching its CD (Consolidated Design) number. N.R. “Woody” Woodward, an authority on collecting glass insulators, devised this identification system. Furthermore, its CD number will reliably identify an item regardless of embossed marks, glass color, or base type.

CD numbers of insulators may be found anywhere on their front skirt, back skirt, or crown. Furthermore, an embossing near the bottom outer edge of their dress is integral to determining its value – often representing end-user companies such as Hemingray, H.G.CO Gregory Insulator Kimble, or others.

Size, rarity, and color all play an essential role in increasing an insulator’s value. Glass insulators in small dimensions are rarely found and are highly sought-after by collectors; similarly, rare colors like cobalt blue and olive green can make these items desirable.

Glass electrical insulators were traditionally installed on telephone and telegraph poles to shield copper wires from heat and lightning strikes, increasing in demand after President Franklin Delano Roosevelt and Congress passed the Rural Electrification Act of 1936 to allow electricity installation across rural America. At first, it was made from mostly glass material but is now increasingly produced from porcelain. These products continue to serve the telecoms industry while becoming more desirable among collectors due to limited supplies becoming more scarce over time.

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