If you’ve been in Pittsburgh for more than a few hours, you’ve definitely seen them.
They’re in basement, bathroom and kitchen windows, of course — odds are you have one in your house. But they also cover shop storefronts. Building lobbies. The sides of warehouses, offices and factories in the Strip. And the platform walls of Steel Plaza T station Downtown.
Glass block windows are seemingly ubiquitous here. But why? And how did Pittsburgh end up with so many in the first place?
It’s likely due to a convergence of factors, including a historical industry, the timing of architectural trends and tastes, and a now-dead local company that once made much of North America’s glass blocks.
Glass city
Pittsburgh boomed as a city of steel. But before there was steel, there was glass — Western Pennsylvania was the center of the U.S. glass industry for about 110 years, from the 1840s to the 1950s.
“It really has been, in many ways, Pittsburgh's hidden industry,” Anne Madarasz, chief historian at the Heinz History Center, said. “And it was all around us.”
@wesanews If you’ve been in Pittsburgh for more than a few hours, you’ve definitely seen them. They’re in basement, bathroom and kitchen windows, of course — odds are you have one in your house. But they also cover shop storefronts. Building lobbies. The sides of warehouses, offices and factories in the Strip. And the platform walls of Steel Plaza T station Downtown. Glass block windows are seemingly ubiquitous here. But why? And how did Pittsburgh end up with so many in the first place? #pittsburgh #pennsylvania #glassblowing #history ♬ Glass cube(1310048) - AZUMAYA
Glass is made from melting sand into a liquid at extremely high temperatures — roughly 3090°F — before it is shaped or molded and then rapidly cooled. And early on, Pittsburgh had a lot of sand that could be dredged from the rivers.
“In the beginning, they used river sand, and eventually they transitioned to mined sand,” Madarasz said.
When the industry began in 1797, Madarasz says the Ohio River linked Pittsburgh to new inland markets that weren’t easily accessible from the East Coast. The War of 1812 subsequently blocked British glass imports, giving the industry time to grow.
Pittsburgh also had abundant local coal and, later, natural gas to fire furnaces at the high temperatures needed for glass, another advantage over eastern glassmakers, which used less-efficient wood as fuel.
As America and the industry grew, Madarasz says it drew in skilled immigrant workers with experience in European glass factories, leading to more and more growth.
“The original factories, their primary product was window glass,” Madarasz said. “You think about the market, as your population in the interior's growing, they need window glass for the homes that they're building. There is no electricity at that time, so glass becomes a light source, and also a light source that allows you to protect against the weather.”
Glass bottles were the second biggest product, followed by simple functional objects like bowls or cups, but Madarasz says the industry eventually moved into more highly valued table objects — think wine glasses, fancy tableware and decanters. By 1902, there were over 100 glass factories in the region.
“These factories were part of the fabric — they were all over the South Side of Pittsburgh; there were some near, you know, kind of what was the Lower Hill,” Madarasz said. “They were part of our city and our identity from some of our earliest times of settlement.”
Just like steel, glass produced in Pittsburgh was meant for the largest economic audience — meaning national and international export.
“You can go to places all over this country and even places around the world and find materials like glass that were made here in Pittsburgh,” Madarasz said.
That includes products from the Pittsburgh Corning Corporation, which was founded in 1937 and would subsequently grow and become America’s largest — and eventually, only — domestic manufacturer of glass block.
“Walls of light”
Elizabeth Fagan is currently a senior landmarks preservationist with the New York City Landmarks Preservation Commission. But she’s also a glass block expert and the author of “Building Walls of Light: The Development of Glass Block and Its Influence on American Architecture in the 1930s” — her thesis for a Master’s degree in historic preservation from Columbia University.
Glass block is made from two pieces of molded glass that are melted together while leaving a hollow, air-filled center. According to Fagan, glass block was invented (and patented) in France in 1886 by Gustave Falconnier, but it looked more like a hexagon and was primarily used in greenhouses.
Blocks similar to what we see today in the U.S. likely came in 1928, with the construction of the Barbizon Plaza Hotel in New York City. The blocks were imported from Germany and used to construct a four-story glass atrium roof, which no longer exists.
Subsequently, Owens-Illinois Glass Company began the first large-scale production of glass block in the U.S. in 1932, and Pittsburgh Corning followed in 1938.
Fagan says the blocks began to be used innovatively as part of Streamline Moderne architecture, which emerged in the 1930s from Art Deco and was influenced by the aesthetics of the machine age.
“Buildings in the Streamline Moderne style were sleek and had these aerodynamic forms, Fagan said. “But this was also the time of the Great Depression, so things were pared back a bit from more elaborate building decorations you had in years past. And glass block was used in this style because it provided visual interest to a building without any additional ornamentation, and it could be used in these long curved walls and sleek lines and big volumetric forms.”
The blocks were also widely used in Modern and International style buildings — typically as flat windows instead of big curves.
“Rather than referencing historic architectural styles, they really embraced machine-made materials and the technology of the future,” Fagan said.
Additionally, glass block was an economical way to update existing buildings, since it was modular and easy to install — it’s a very similar process to laying brick and mortar. It was also mass produced, came in a variety of sizes and patterns, and provided insulation and soundproofing while letting light through.
During the day, that brought sunlight in with privacy. But at night?
“You could light this building up from within and it turned the building into a beacon or an advertisement,” Fagan said.
Because of that, Fagan says glass block was extensively used in commercial architecture — think buildings like department stores, movie theaters and gas stations.
“When these buildings were lit up at night, you could show off that you were modern and up to date with new technology,” Fagan said.
But as the 1940s went on, architectural tastes moved towards the Mid Century Modern and International styles, and thus away from lots of glass block in big commercial projects. Instead, Fagan says it transitioned to being widely used in schools and homes, and was marketed to middle-class American homeowners as a way to update (and modernize) those spaces.
“It was geared towards smaller applications, like adding light above your kitchen sink or putting privacy in a bathroom window,” Fagan said.
And many of those blocks were made by Pittsburgh Corning.
Pittsburgh made
Although glass block originated with Owens-Illinois, Pittsburgh Corning spent decades as the only remaining domestic manufacturer. But the company faced challenges, like the rest of the city’s glass industry, which began to decline after the 1950s.
Madarasz says much of that was due to competition from overseas manufacturers with access to cheaper labor and fuel sources, as well as the raw materials. Additionally, the development of glass alternatives like paper cups, Styrofoam, aluminum cans and plastics also contributed as they took over sections of the market.
”When we opened our exhibit here at the History Center on glass, Glass Shattering Notions, in 1998, there were about two dozen producers in the region of glass. I would say today, maybe there's four or five,” Madarasz said. “You still have artist studios, things like the Pittsburgh Glass Center. But in terms of industrial production, it's been a big change in just that period from 2000 to where we are today.”
Pittsburgh Corning held on longer than most, but entered Chapter 11 bankruptcy in 2000 after a separate division that produced asbestos insulation materials faced mounting exposure-related lawsuits.
After a complicated, 16 year process, Pittsburgh Corning exited bankruptcy in 2016. The company subsequently ended all glass block production and shuttered its Port Allegany facility, which had been operating for 79 years.
Steve Boesch is the vice president of GBA, a Medina, Ohio-based company that has been distributing glass block since 1985. He says that the bankruptcy killed Pittsburgh Corning’s glass block business.
“When they were in Chapter 11 bankruptcy protection, they didn't do anything to advance the quality and technical advantages of glass block,” Boesch said. “They were so far behind all the engineering techniques and everything else that they really weren't able to recover.”
At the time, GBA was Pittsburgh Corning’s largest distributor.
“We used to buy about $3.5 million of glass block from Pittsburgh Corning a year,” Boesch said.
After the bankruptcy, Boesch says GBA bought up a lot of the company’s remaining inventory so they would have ample supply until they secured a new source from overseas — he says glass block now comes from factories in Europe, Indonesia and China.
They ended up with about 75 shipping containers worth of products, and are down to around 8 left.
But despite the local history, Boesch also notes that Pittsburgh is not actually the top place for glass block — it’s Chicago. Pittsburgh, by contrast, ranks up with Cleveland and Detroit as a major spot for the material.
As to why there’s still so much here, it may just be the intersection of trends and durability.
Boesch says the popularity of glass block comes in waves. It was “real big” in the 1950s (especially in schools), then again in the 1970s (with the New York Times proclaiming that “Glamorous Glass Bricks Are Booming”), and again in the 1990s.
And since glass block is a low maintenance material that is cemented into walls, it can stick around for a long time.
“As long as you do it right, use the right mortar, perimeter sealants, all that; glass block will typically give you a 50-year life cycle without much problem at all,” Boesch said.
He also credits the material’s properties for its long-lasting popularity.
“Insulating value. Light transmission. No maintenance. Durable. Security. Aesthetically pleasing. Economical. You know, has LEED qualifications because it's all recyclable,” he said. “That's quite a few there.”
Fagan believes glass block’s endurance goes back to its very nature.
“You know, how trends evolve is maybe a mystery sometimes,” Fagan said. “I guess I can say without touching on specific time periods, I think architects and designers perhaps liked the light-giving qualities that glass block provided, and that's a timeless feature.”
