How architect John Ronan engineered a glass memorial built to endure for centuries

When the Fallen Journalists Memorial is complete, light will pass straight through it as the sun moves across the National Mall, shimmering across two hundred fifty tons of glass and making it the first all-glass memorial ever built there.

But don’t mistake that for fragility.

People often hear “glass memorial” and picture something that could be knocked over, cracked, or swept away. That instinct is exactly what architect John Ronan has had to work through with the agencies reviewing the design, making the case that a solid, 836-pound cast block is sturdier than stone. “It’s common to think of glass as being very fragile,” he said. “You have to overcome that perception.”

The material he’s using is called cast glass, and it behaves nothing like the glass in a window. Float glass—the kind in your house—is a thin sheet formed by dragging molten glass across a bed of liquid tin. Cast glass is different: it’s melted at extreme temperature and poured directly into a mold. Then it’s annealed, or slowly cooled, over days or weeks, so the block doesn’t crack from stress trapped inside as it cools. What comes out is a solid, dense block instead of a thin sheet.

“It’s denser than stone, and heavier than concrete, because concrete has some air in it,” Ronan said. “There’s no piece of glass ever made by man that has disintegrated. They’ve found glass at the bottom of the ocean, on sunken ships, that’s over two thousand years old, and it’s intact.”

But permanence isn’t the only variable. Washington is known for its four distinct seasons—humid summers pushing past 90 degrees, winters that drop below freezing, and days where a cold morning can give way to an afternoon heat wave. Ordinary glass hates that. Rapid changes in temperature can crack it.

Ronan’s solution is a specific formulation called borosilicate glass, invented by the American glassmaking company Corning roughly a century ago by introducing boron into the glass mix.

“Pyrex is a form of borosilicate glass,” he said. “You can take a Pyrex container out of the refrigerator and put it in your oven, and it won’t crack. Normal glass will crack if you change the temperature quickly. Borosilicate glass will not.”

Borosilicate is more commonly found in lab equipment, medical instruments, and telescope lenses than in architecture, which is part of what makes this application unusual.

The scale compounds the engineering problem. The cast elements in the design run 8 inches by 12 inches in cross-section and 8 feet long, and each one weighs more than a ton. Rather than binding the blocks together, Ronan’s team is stacking them on top of each other, with only a thin bearing pad between each layer to absorb shock and distribute the load.

“These things are so heavy that the wind is not going to push them,” Ronan said. “You would have to run a tank into them to displace them.” That density, he added, is what gives the stack its lateral stiffness, with no fasteners required—just mass resting on mass.

What began as a box of gourmet ice cubes in a Chicago studio is becoming a permanent structure on the National Mall: cast borosilicate glass, engineered to survive Washington’s seasons and to still be standing, unclouded, centuries from now. It’s a fitting material for a memorial to journalists, built to hold up under pressure, and to let the light through anyway.

Learn more about supporting the memorial at fallenjournalists.org.