Opinion: The Opacity of Glass

By Aki Ishida, AIA 

The word “local” has become synonymous with sustainability. Whether it is the food we eat, the clothes we wear, or the materials we use to construct our buildings, those who are mindful of sustainability are attuned to where our ingredients and materials come from. While we can go to a local hardware store, or even a Home Depot, and find bags of cement that come from an adjacent county, or lumber from a local sawmill, we don’t think to ask for “local glass.” The source of glass sheets is often unknown beyond the brand logo etched on a corner, such as Cardinal Glass or Vitro (formerly PPG), which have plants all over the country or the world. The sources of the raw materials, such as sand, which makes up over 70 percent of glass, are even less known.  

GLASS PRODUCTION IS RARELY LOCAL 

For nearly a decade, I taught a building materials class at Virginia Tech; it was a required course for all sophomore architecture students. While introducing the properties of basic construction materials, I took students to local brick plants and stone quarries. Walking through a brick plant in Roanoke, Virginia, the plant managers pointed to the reddish soil beneath their boots and the surrounding wooded landscape, and the students understood why the brick plants are located where they are and why we see many brick buildings in this region. When visiting a stone quarry owned by Virginia Tech where they mine “Hokie stone,” a grey limestone that wraps nearly every new building on campus, the students saw firsthand that limestone is a limited, natural material that is extracted from the earth.  

Glass is different. While there are nearby manufacturing plants that assemble windows and doors, the nearest float glass production plant, which I visited while developing the course, is the Pilkington plant in Laurinburg, North Carolina, 250 miles south of campus. Named after Alastair Pilkington, who invented the float glass manufacturing process in 1952, Pilkington is a major global producer of architectural glass. It has just five production plants in the U.S.: one in Laurinburg, two in Ohio, and one in Illinois. Besides the availability of fuel, skilled labor and transport infrastructure, the locations are tied to the industries they serve: furniture production in North Carolina and automobiles in the Great Lakes region. By comparison, General Shale, the country’s largest manufacturer of bricks, has 28 plants across the U.S. and Ontario, Canada.1 Masonry plants are localized, situated where shale is found, whereas glass plants, which are more costly and energy intensive to build and run, are spaced farther apart. Before glass plants became centralized in a few locations, more small plants were located adjacent to sand mines. For example, a glass plant in Crystal City, Missouri, was located next to St. Peter Sandstone, but was closed in 1990 when they could not afford to modernize the plant. As a result, sand travels long distances to get to the plants.  

Our propensity to build with glass continues to grow despite the material’s link to solar heat gain and the climate crisis. Unsustainable aspects of architectural glass are not limited to high heat transmission but also the difficulties in recycling architectural glass (largely due to the labor involved in separating glass from the building assembly), greenhouse gas emissions during production and the extraction of sand. Although glass is touted as an “infinitely recyclable material,” only 6 percent of architectural glass is downcycled into glass products that require less purity and precision.2 Almost none is recycled into architectural glass,3 and the rest ends up in landfills.  

The process by which sand — whether from a riverbed, a lakeshore, or an inland limestone outcrop — becomes sheets of glass is far from transparent. While we think of architectural glass as a human-made material of the Industrial Age, its raw materials—silica sand, soda ash, and limestone—are natural, extracted from the earth and not renewable. Sand with at least 95 percent silica content is called silica sand, and only the purest is suitable for architectural glass production. Such sand is found in limited areas, and the ultra-pure sand required for low-iron glass is even more rare.  

The mysteries of glass production have historic precedent that can be traced back to trade secrets of the Venetian Empire. Venice became the center of glass production largely due to its strategic location for importing raw materials and exporting coveted glass objects. From the 11th to the 16th centuries, the secrets of glassmaking were protected by the Venetians. Then three glassmakers were smuggled out by King Louis XIV of France, who applied the coveted technology to realize Versailles’ Hall of Mirrors.  

The islands of Venice and Murano were otherwise unlikely locations for glassmaking. Neither the primary materials of sand and soda ash (sodium carbonate) nor the fuel for the medieval Venetian glassmakers were found in the immediate vicinity. Sand was transported from the riverbeds of the Ticino River in Switzerland and the Agide River in Italy, which flows from the Austria-Switzerland border to the Adriatic Sea south of Venice. Soda ash, which is needed to lower the melting point of silica sand, was brought from Syria and Egypt.4 In other words, Venetian glass production depended not on the abundance of native materials but on precious resources imported from afar on ships. In addition to its historic preciousness, glass’s unusual material properties amplify its enigma.  

WHAT GLASS MEANS 

Glass is neither liquid nor solid. It is amorphous. Sand, along with other minerals, is heated to reach a liquid state, then cooled to an amorphous solid, which hovers between the two states. Glass is often a metaphor for transformation in people, perhaps because the process of making glass involves the transformation of an ordinary material — sand — into an extraordinarily delicate, crystalline material.5 In the fairy tale of Cinderella, the glass slipper she loses at midnight comes to symbolize exquisite beauty and transforms a maid into an object of desire. In early modern sanatorium buildings, including the Zonnestraal (1931) [Figure 2] in the Netherlands, it was believed that solar transmission through the glass walls would “heal” sick tuberculosis patients, turning them into healthy workers. 

Contemporary architects and designers have specified glass for its transparent material properties as well as its cultural meanings, including magic, prestige, and political transparency. In the late 20th and 21st centuries, the transparency of glass has often been appropriated to symbolize openness, accessibility, and freedom. Glass in the Louvre Pyramid by I. M. Pei6 and the Reichstag renovation in Berlin by Norman Foster is often associated with democratic government. For the company Apple, glass has become fundamentally linked with their products and architecture, from all-glass iPhones to flagship stores featuring expensive and daring experiments in architectural uses of glass, such as the emblematic structural glass stairs [Figure 1] first completed in Soho, New York in 2002.7  

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The opacity of glass production contributes to over-consumption of glass. Local production of glass becomes more difficult as we increasingly demand glass that is colorless, extra-large, and seamless. Highly pure sand required for low-iron glass can only be mined from limited locations, which results in long-distance shipping. Production and fabrication of extra-large glass panels can only be done at a limited number of plants in the world, which increases the carbon footprint. Extra-large panels also require specialized labor and equipment, which may not be available locally. By becoming better educated about where the raw materials for glass come from and how they are produced, we can bring more transparency to glass production and contribute to more sustainable uses of glass in architecture.  

AKI ISHIDA, AIA, LEED AP, is the director of the College of Architecture and Graduate School of Architecture & Urban Design at Washington University in St. Louis and the author of Blurred Transparencies in Contemporary Glass Architecture: Material, Culture, and Technology.  

Citations 

1. “General Shale Becomes North American Market Leader, General Shale, accessed July 4, 2025, https://generalshale.com/newbrandnetwork/  

2. Graham Coult and Stéphany Le Rhun, “How reusing and recycling glass can cut a building’s carbon emissions,” March 5, 2024, RIBA Journal, accessed July 4, 2025, https://www.ribaj.com/intelligence/materials-book-glass-reuse-recycling-architecture#:~:text=Recent%20best%20practice%20has%20only%20resulted%20in,as%20glass%20bottles%20and%20glass%20wool%20insulation.  

3. Graeme DeBrincat and Eva Babic, Re-thinking the life-cycle of architectural glass (Glasgow: Arup, 2018).  

4. “Glass as a Material in Renaissance Venice,” Corning Glass Museum, accessed July 3, 2025, https://renvenetian.cmog.org/chapter/material-making-glass-renaissance-venice.  

5. Carina Hart, “Glass Beauty: Coffins and Corpses in A. S. Byatt’s Possession,” Marvels & Tales 26, no. 2 (2012), 205.  

6. Annette Fierro, The Glass State: The Technology of the Spectacle, Paris, 1981–1998 (Cambridge, MA: MIT Press, 2003), 171. 

7. Aki Ishida, Blurred Transparencies in Contemporary Glass Architecture Material, Culture, and Technology (New York: Routledge, 2020). 

CAPTIONS: 
Figure 1: Glass stairs inside the Apple Store in Soho, New York  
PHOTO: TRIPYRAMID STRUCTURES   

Figure 2: Zonnestraal Sanatorium, Hilversum, Netherlands 

PHOTO: AKI ISHIDA