The Invisible Blue-Jean Particles in the Original Star-Spangled Banner

The American flag at the Smithsonian has collected blue cotton fibers over the years, but not as many as popular legend says.

If you’ve visited the National Museum of American History in the last century, you may have seen one of its most prized artifacts: The original star-spangled banner—the one that Americans raised at Fort McHenry to celebrate their victory over the British in the War of 1812.

It was the sight of this gigantic flag, sewn by Mary Pickersgill, that inspired Francis Scott Key to write “The Star-Spangled Banner.”And maybe you’ve heard about one of the biggest threats to the flag’s longevity. Over the second half of the 20th century, the story goes, this national treasure’s aging fabric was being infiltrated and deteriorated by tiny blue cotton microparticles—invisible-to-the-eye bits of denim that came from the jeans worn by tourists who visited the museum to admire the flag.

It’s sort of romantic, this idea that little bits of blue jeans worn by the American people might be embedded in the flag itself. That’s probably why so many people believed the story.

“But it was never proven to be blue-jean dust,” said Suzanne Thomassen-Krauss, chief conservator of the most recent Star-Spangled Banner Preservation Project. “It’s been a persistent myth from the ’70s. When we examined some of the fibrous debris of the flag, we did find blue cotton fibers. However, we found even more white cotton fibers, so it could have been from anything—not just blue jeans. And the amount of blue fibers compared to the white fibers was very, very low.”

The more likely culprits of foreign fibers found on the flag, she says, are cleaning rags, mops, papers, and shirts. The flag was also covered in particles of aluminum and calcium silicate, bits of gypsum board, cement, and concrete.

When it was new, the star-spangled banner—this one has 15 stars and 15 stripes—spanned 30 feet by 40 feet and weighed some 50 pounds. The Smithsonian has had the flag since 1907, and preservation efforts, all driven by technologies of the time, have evolved dramatically over the years. In the 1960s, the Smithsonian opted to put the flag in the only Smithsonian building that was air conditioned, thinking the cool temperature would help preserve the aging flag. But in the most extensive conservation project in the flag's history, conservationists like Thomassen-Krauss found that exhibits designed to protect the flag were in fact doing the opposite.

“Negative pressure inside the building meant we were sucking inside all the construction debris and pollution from outside,” Thomassen-Krauss told me. So even after museum staffers placed the flag behind a protective screen in the 1980s—the screen would drop for one minute every half-hour so visitors could catch of glimpse of Old Glory—the flag itself was essentially acting as an air filter for all the dirt and dust that floated through the building.

“If you move air and it has particulates in it and it meets a resistance, it's going to deposit the material,” Thomassen-Krauss told me. “Part of it was there was an environmental system designed for that space to keep the environment more stable around the flag, but in reality, because of the negative pressure, it was creating positive pressure behind the flag—kind of making the dirt move back and forth—so there was associated soiling.”

After 10 years of meticulous conservation work, the flag was put back on display in 2008—this time in a temperature controlled room with a high-tech filtration system that keeps tiny particles out.

“We’re always limited by the technology that’s available,” said Thomassen-Krauss. For many years, the Smithsonian couldn't build a glass case big enough for the entire flag, so only a quarter of it was on display. Today, museum staffers considered using a giant pane of glass that has an electric current running through it, so that it can be made opaque or transparent. (Ultimately, they decided not to use it.) The high-efficiency particulate air filter in the room that houses the flag today wouldn’t have been available to the conservationists before Thomassen-Krauss’s time. “Twenty years ago you would have only found that on vacuum cleaners designed for hazmat conditions for cleanups. That would have been a very, very expensive piece of equipment for anyone to purchase.”

“We hope the current exhibit is going to last at least a generation or many generations,” she said. “But if something new comes out tomorrow, we'll consider it. Every time someone says, ‘I think we can do better,’ we try to incorporate new things. You try and anticipate what will happen in the future, but you can never know.”