Glass Insulators: A Collector’s Introduction to America’s Most Overlooked Antique

Glass insulators are the colorful glass fittings once used on telegraph, telephone, and power lines across North America. Today they are popular collectibles because of their history, variety, and affordability. The Bolack Museum Foundation in Farmington, New Mexico, preserves what it describes as one of the world’s largest glass insulator collections, assembled over a lifetime by Tommy Bolack.

Glass insulators spent more than a century performing a practical job on utility poles, then quietly became one of America’s most accessible collecting hobbies. While many antiques require significant investment or specialized knowledge, glass insulators offer an approachable entry point into collecting, with common examples available for just a few dollars and rarer pieces prized for their colors, shapes, and history.

If you’d like to see an insulator collection at its highest level, the Bolack Museum Foundation preserves what it describes as one of the world’s largest assemblages of glass insulators. You can plan your visit to view the collection in person on the B Square Ranch in Farmington, New Mexico.

What Are Glass Insulators?

Key takeaway: Glass insulators are molded glass fittings that held telegraph, telephone, and power lines away from utility poles while preventing electricity from leaking into the supporting structure.

Glass insulators were once a common sight along roads, railways, and rural utility corridors throughout North America. Mounted on wooden pins attached to utility poles, they supported electrical wires while insulating those wires from the pole itself.

Their earliest use was on telegraph lines during the 19th century. As communication networks expanded, telephone systems adopted similar designs. Electric utilities later relied on glass insulators for portions of their power-distribution infrastructure.

Glass offered several advantages. It was relatively inexpensive to manufacture, weather-resistant, durable outdoors, and an effective non-conductor. Millions were produced by American manufacturers during the late 19th and early 20th centuries.

As utility systems modernized, glass insulators gradually disappeared from active service. Many were discarded during line upgrades, but others were salvaged and preserved by collectors who appreciated both their historical significance and visual appeal.

Today, insulator collecting remains an active hobby supported by organizations such as the National Insulator Association, which helps document, research, and preserve the history of these once-common pieces of utility hardware.

A Short History of the Glass Insulator

Key takeaway: Glass insulators served on telegraph, telephone, and power lines for roughly a century before collectors preserved them as historical artifacts.

The story of glass insulators begins with the expansion of telegraph networks during the mid-19th century. Samuel Morse’s successful telegraph demonstration in 1844 helped launch a communications revolution that quickly spread across North America. As telegraph lines multiplied, utilities needed a reliable way to keep wires insulated from supporting poles.

Manufacturers responded by producing specialized glass insulators designed for outdoor use. Demand grew further when telephone networks expanded during the late 19th century.

The rise of electric power systems created another major market. By the early 20th century, glass insulators appeared on utility poles throughout cities, towns, and rural communities. The Rural Electrification Act of 1936 accelerated this growth by extending electrical service to previously underserved areas.

Usage peaked between roughly 1920 and 1950. Over time, utilities increasingly adopted porcelain and other materials that offered advantages for certain applications. By the late 1970s, glass insulators had largely disappeared from new installations, and many communication systems no longer required them.

As old lines were removed, collectors began saving the discarded hardware. Organized insulator collecting gained momentum during the 1960s and eventually led to the creation of hobby organizations and reference resources. Sites such as insulators.info now help collectors identify and research antique insulators from around the world.

Types, Shapes, and How Collectors Identify Them

For newcomers, one of the first surprises is how many different types of glass insulators there are. Collectors classify pieces using several systems, but the most important is the CD (Consolidated Design) numbering system.

Created by N.R. “Woody” Woodward, the CD system categorizes pin-type insulators by shape and profile rather than color or manufacturer. This gives collectors a common language for describing pieces.

The most common design is CD 154. Within that category, the Hemingray-42 is often considered the single most common glass insulator in North America. Many collectors begin their collections with one.

Collectors also use informal shape names such as “beehive” and “pony.” These nicknames make it easier to discuss broad categories of insulators without relying entirely on CD numbers.

Manufacturer markings provide another important clue. Companies such as Hemingray, Brookfield, Whitall Tatum, and McLaughlin embossed their names, initials, or production markings into the glass. Collectors often use these markings to identify production periods and manufacturing origins.

For beginners, the most important lesson is simple: shape, CD number, manufacturer, and embossing are the primary tools collectors use to identify and organize glass insulators.

Visitors interested in seeing examples spanning hundreds of styles can explore the collection housed within the Tommy Bolack Electromechanical Museum, where tens of thousands of insulators illustrate the scale and diversity of Tommy’s passion.

What Makes a Glass Insulator Valuable?

Many newcomers wonder about glass insulator value. The answer depends on four primary factors: color, rarity, condition, and manufacturer.

Color is often the first characteristic collectors notice. Clear and aqua examples are the most common because they were produced in large quantities. Rarer colors tend to command greater interest among collectors.

Among vintage glass insulators, cobalt blue remains one of the most sought-after colors. Amber, purple, olive green, and certain unusual shades can also attract significant collector attention.

Condition matters as well. Chips, cracks, staining, and repairs generally reduce value. Collectors typically prefer pieces that remain in original condition.

The manufacturer and rarity play equally important roles. Common Hemingray examples may sell for only a few dollars, while scarcer production runs, unusual embossings, or rare color combinations can be worth considerably more.

As a general rule, the most common glass insulators and antique insulators often sell in the range of roughly $5 to $20. More desirable examples can reach into the hundreds of dollars, while a small number of exceptional rarities have sold for substantially higher amounts.

New collectors should also be cautious. Some pieces have been altered through heat or radiation treatments to create unusual colors. For higher-value purchases, it is wise to consult experienced collectors and established reference organizations before buying.

Tommy Bolack and One of the World’s Largest Insulator Collections

The authority behind this article comes from the collection itself.

According to the Foundation, Tommy Bolack’s interest in glass insulators began when he was five or six years old. During a family trip to Kansas, he gathered a shoebox full of insulators and brought them home. That childhood interest became a lifelong passion.

Over the decades, Tommy Bolack assembled what the Foundation describes as one of the world’s largest glass insulator collections. The collection became part of a museum complex exceeding 40,000 square feet on the B Square Ranch near Farmington.

The scale is difficult to visualize. The collection includes a massive outdoor accumulation of common aqua glass insulators alongside curated displays of rare and unusual examples from North America and abroad. Tommy Bolack became known as a serious CD collector who pursued both domestic and international pieces.

His involvement in the hobby extended beyond collecting. He hosted the National Insulator Association’s national show in Farmington in 2014 and remained active within the collecting community for many years.

Tommy Bolack earned an electrical technology degree from New Mexico State University and applied that technical knowledge throughout his work on the ranch and museum properties.

After Tommy Bolack passed away in 2024, the collection remains preserved through the charitable Foundation he helped create. Today, visitors can learn more about Tommy Bolack and his family’s legacy while exploring the collection exactly as he intended it to be experienced and displayed.

See the Collection for Yourself

One of the world’s largest glass insulator collections is located at the Tommy Bolack Electromechanical Museum on the B Square Ranch, 3901 Bloomfield Highway, Farmington, NM 87401.

The Foundation’s current  museum hours are Monday through Saturday from 9 a.m. to 3 p.m. Mountain Time, although visitors should confirm current schedules before traveling. Admission is free, reservations are recommended, and access is provided through guided tours. [FLAG 1]

The museum gives collectors, history enthusiasts, and anyone curious about one of America’s most unusual collections a chance to see the history of glass insulators. For current information, directions, and reservations, plan your visit through the Foundation’s visitor information page or call 505-325-4275.

Frequently Asked Questions

What are glass insulators and what were they used for?

Glass insulators are molded glass fittings designed to support electrical wires while preventing current from flowing into utility poles. They first appeared on telegraph lines during the 19th century and later became common on telephone and electrical distribution systems. Mounted on pins attached to poles, they helped keep wires elevated, separated, and insulated. Glass was widely used because it was durable, inexpensive to manufacture, and resistant to weather. Although utilities eventually replaced most glass insulators with other materials, millions remained in circulation and many were preserved by collectors.

Why do people collect glass insulators?

Collectors are drawn to glass insulators for several reasons. They combine industrial history, attractive colors, and a wide variety of shapes and markings. The hobby is also accessible because many common pieces remain affordable. Some collectors focus on manufacturer markings such as Hemingray or Brookfield, while others specialize in colors, CD numbers, or regional history. Organized groups, including the National Insulator Association, support research and collecting activities. Many enthusiasts also enjoy the challenge of finding rare examples among pieces that once served as ordinary utility hardware.

How can you tell if a glass insulator is valuable?

Value is primarily determined by color, rarity, condition, and manufacturer. Clear and aqua insulators are generally the most common and often have modest values. Colors such as cobalt blue, amber, purple, and olive green tend to attract greater collector interest. Condition is important because chips, cracks, and repairs can reduce value significantly. Rare embossings, unusual CD numbers, and limited production runs may increase desirability. Most common examples are worth only a few dollars, while scarcer pieces can reach into the hundreds. Exceptional rarities may command substantially higher prices in specialized collecting markets.

How do collectors identify glass insulators?

Collectors primarily identify glass insulators through the CD, or Consolidated Design, numbering system. The system classifies pin-type insulators according to shape and profile, allowing collectors to compare examples regardless of color or manufacturer. Embossed markings provide additional information. Names such as Hemingray, Brookfield, Whitall Tatum, and McLaughlin often appear directly on the glass. The Hemingray-42, classified as CD 154, is widely considered the most common insulator in North America. Together, CD numbers, manufacturer markings, color, and physical characteristics help collectors accurately identify and catalog pieces.

Are glass insulators still used today?

Glass insulators are rarely used in modern utility systems. During the second half of the 20th century, many companies transitioned to porcelain and other materials for various applications. Advances in communications technology also reduced the need for traditional pole-mounted insulators. By the late 1970s, glass insulators had largely disappeared from new utility installations. Today, most examples survive as historical artifacts, collectibles, or museum pieces. While a few may remain in service on older infrastructure, the vast majority are now valued for their historical significance rather than their original function.

Where can you see one of the world’s largest glass insulator collections?

According to the Foundation, the world’s largest glass insulator collection is preserved at the Tommy Bolack Electromechanical Museum on the B Square Ranch in Farmington, New Mexico. The collection was assembled over a lifetime by Tommy Bolack and includes both common and exceptionally rare examples. Admission is free, though reservations are recommended to secure a spot on a guided tour. Visitors can obtain current scheduling information through the Foundation’s visitor information page or by calling 505-325-4275. The collection provides a unique opportunity to see the history of glass insulators represented on an extraordinary scale.