Black splotches have appeared on the Jefferson Memorial and a hallowed shrine at Arlington National Cemetery, leaving experts baffled at what has caused this outbreak of biofilm, the Los Angeles Times reported on Wednesday.
Biofilm is also starting to emerge at several other noted places in the capital, including the Washington Monument and Lincoln Memorial, though they have not yet been visibly marred.
National Park Service historic architect Audrey Tepper, who is overseeing the effort to remove the splotches, said, “We’ve never seen it before. Now it is everywhere.”
In general, biofilm remains one of the great scientific mysteries, with experts unable to explain how and why it emerges in so many types of places and apparently for a varied number of reasons.
In the case of Washington’s storied monuments, the National Park Service is examinng how and why the biofilm got there, how aggressively to scrape it off, and how likely the discoloration will spread.
“Nothing is ruled out,” said Judy Jacob, a senior Park Service conservator. “Everything is possible.”
Great care is being taken, because preservationists regret the damage done when chemical agents were used to scour historic marble buildings in Italy, France and the U.S. decades ago.
Using zinc oxide has also been ruled out, even though it is proving effective at restoring blemished stone near the Tomb of the Unknown Soldier. This is because the risk is too high at the Jefferson Memorial, where the inorganic compound could leech into the nearby Tidal Basin.
Instead, experts are methodically burning the film off the dome with handheld lasers, which takes an hour to clean two square feet. The budget is more than $8.7 million.
However, no one can guarantee that biofilm won’t stain the dome again once the job is finished or that it won't attack other historic marble buildings.