The material, glass, is itself an insulator (not a “conductor” or “transformer” as insulators are often incorrectly labeled in antique malls and flea markets).Both glass and porcelain insulators have been used since the early days of the telegraph, but glass insulators were generally less expensive than porcelain, and were normally used for lower-voltage applications. The period from 1875 to 1930 might generally be thought of as the “heyday” of the glass insulator.
Dating whitall tatum glass insulators
From undated real photo postcard, Joliet, Illinois, circa 1909.
" data-medium-file="https:// data-large-file="https:// class="wp-image-1563 size-large" title="Telegraph pole with glass insulators, near Joliet IL, circa 1909" src="https:// alt="Telegraph line pole with glass insulators " width="640" height="780" srcset="https:// https:// sizes="(max-width: 640px) 100vw, 640px" / During the 1960s, 1970s and 1980s many of these lines were dismantled as technology advanced.
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Long before the modern era of computers, cellphones, smartphones, fiber-optic cables and the internet, long distance electric/electronic communication consisted primarily of the telegraph and telephone.
Most insulators are found in some shade of blue-green/aqua-colored glass (typical cheap “bottle glass” or “green glass”) but many, many other color shades are found.