The year is 2017. For more than a decade, the white marble of the Thomas Jefferson Memorial has been blighted with a darkening effect that continues to spread.

The culprit? Biofilm—colonies of microscopic organisms whose only creed is to multiply and whose favorite surface is stone. It started at the memorial’s dome and hasn’t let up.

In 2014, the National Park Service brought together a crack team of conservators, architects, and other experts to find a solution. Two years later, the agency put out a call for the best damn cleaning method it could find, scouring options for their prowess against the biofilm, but also for its effect on the memorial’s marble and the surrounding environment. Whoever took up this task had to be lethal, no doubt, but gentle, too.

An unexpected hero emerged: lasers.

Starting in September, NPS began a four-week pilot program to test the laser ablation process on 1,000 square feet on the memorial’s northeast side. It involves fine-tuning a laser to irradiate material like pesky biofilm from a surface, and Chicago-based conservation firm Conservation of Sculpture and Objects Studio, Inc. conducted the test.

“We’re very satisfied with the results of this laser ablation test,” said Architectural Conservator Justine Bello in a release. “The level of clean that was achieved exceeded our expectations. We were able to clean the stone in a safe manner that protected both this cultural resource and the surrounding natural environment as well.”

So 1,000 square feet down, and 9,682 to go. NPS says it plans to finish irradiating the memorial alongside a project to rehabilitate the Jefferson Memorial roofs in 2018. NPS spokesperson Mike Litterst says it’s too early in the process to say whether that work will require closures for the memorial, though “the goal would be to not limit access.”

Which brings us to this story’s forthcoming sequel: getting that project as requested through the FY18 park service budget.

NPS says visitors will be able to see the difference the lasers have already made as the scaffolding comes down this week.

Previously:
Frickin Laser Beams Will Clean Grime Off Jefferson Memorial