Good news has been reported by those engaged in the struggle to preserve one of Washington’s most iconic monuments against the ravages of a kind of microscopic predator: biofilm.
The National Park Service has announced success in the four-week test run of a technique to remove the stubborn layer of black and gray film that has increasingly besmirched the white marble dome of the Jefferson Memorial.
In an announcement Tuesday, the NPS said its test of a process called laser ablation has cleared the unsightly layer of microbial matter from 1,000 square feet of the monument’s dome. That is about a tenth of the total area of the dome.
“We’re very satisfied with the results” of the laser ablation test, said architectural conservator Justine Bello. “The level of clean that was achieved exceeded our expectations,” she said.
One of the major challenges in architectural restoration is removing the objectionable material while preserving the structure that it has covered and protecting the environment in which the structure is located.
In laser ablation, laser energy heats the undesirable gunk, which evaporates into the air, leaving the underlying stone intact.
As scaffolding is removed, according to the park service, the evidence of restoration should become visible to visitors to the Tidal Basin of seeming victory in the grinding battle against one of the most dogged and persistent natural enemies of stone structures.
Biofilms consist of clumps of microorganisms that cling to each other and to stone surfaces as well. Humid environments assist their growth. The films have proven to be as difficult to remove as they are disagreeable to see.
The colony of pernicious microorganisms was first detected on the memorial’s marble in 2006. Studies have been under way since 2014 to find the best way of getting it off. Over the past year, a search has been conducted for the most desirable treatment.
According to the park service, it reviewed potential products and processes numbering in the hundreds. Candidates needed to meet the threefold test, of ridding the marble of the film, while saving the stone and doing no harm to the monument’s surroundings.
When conducted by specially trained personnel who can fine tune lasers to suit both the type of stone and the type of film, the park service said, laser ablation permits safe film removal, while making it unnecessary to deploy abrasives or harsh chemicals.
With the test a success, the park service said, it contemplates removal of the biofilm from the remainder of the time. The park service said it had tentative plans to do the job next year while it rehabilitates the monument’ss roof areas.
The roof project is in the park service’s requested budget for fiscal year 2018, the NPS said.
The laser ablation test was conducted by Conservation of Sculpture and Objects Studio, Inc., a Chicago-based conservation firm, NPS said.