Glass block

Glass block is a type of structural glass that gained popularity in the first half of the 20th century when styles like Art Deco, Streamline, and Art Moderne were in vogue. Glass block frequently shows up in both interior and exterior walls in industrial, commercial, and even residential architecture of the 1930s and 1940s.

A glass block is hollow but sturdy, typically ranging from eight to 12 inches square and four inches thick. Though not strong enough to be used in loadbearing walls, a glass block has a compressive strength ranging from 400 to 600 pounds per inch. As a result, glass block acts as a superb insulating material and sound barrier. Like all glass, it can chip or crack, but it tends to be much more resistant to damage than plate glass.

Many manufacturers touted the functional applications of glass block, including the various patterns available to help diffuse daylight inside a building (a function that dates back to the 19th century with vault lights or “sidewalk prisms” to illuminate basements and cellars). Besides its function, glass block was also marketed as architectural flair. An Insulux Glass Block ad described its product as “mainly a design element to add decorative beauty” that takes “full advantage of the fluidity and translucence of glass.” Mechanic shops, restaurants, bars, and movie theaters are only a few of the business types that used glass block for both practical and atmospheric reasons.

The first photo shows the Callender Block in downtown Livingston, with a band of structural glass block added in the 1940s to a building originally built in 1906. The second photo shows damage to a glass block on a historic business in Lewistown’s commercial historic district.

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