Golden-brown moss had crept up the sides of the headstones, surrounding the chiseled letters whose edges had been softened by many years of sun and wind and rain.

For an hour and a half Thursday afternoon, two men knelt in the grass of Leesburg’s Mount Zion Cemetery and carefully cleansed the gravestones of four Civil War veterans from Loudoun County, transforming the time-worn granite that marks their resting places.

The veterans honored Thursday were Joseph Waters of the 5th Massachusetts Cavalry; James Gaskins of the 39th U.S. Colored Infantry; William Taylor of the 1st U.S. Colored Infantry; and John Langford, a Union Navy sailor. The four men were among the hundreds of African American Civil War soldiers from Loudoun, of whom only about 20 returned to the county after the war, said Kevin Grigsby, a local historian who published the book “From Loudoun to Glory” last year to chronicle the role of African Americans in Loudoun during the Civil War.

“These soldiers have kind of been forgotten,” Grigsby said. “You don’t hear a lot about them.”

The Loudoun County Sesquicentennial committee is hoping to help change that, he said, by establishing an official Civil War marker at Mount Zion Cemetery. A memorial ceremony is planned for Sept. 6, Grigsby said.

To prepare for that event, the committee first wanted to clean the soldiers’ gravestones. Although Mount Zion is a well-tended cemetery, Grigsby said, the stones have been unavoidably weathered over many decades.

Knight Solutions, a Leesburg construction company that builds and renovates national cemeteries, volunteered to do the restoration work.

James Johnson, director of field operations for Knight Solutions, did the restoration work with a colleague, using a special cleansing solution to soak the headstones and loosen the dirt and moss. A hand-held power washer blasted away the residue, yielding dramatic results, Johnson said.

At most national cemeteries, Johnson said, “we’re required to clean the headstones once a year, so often you don’t even notice a difference. You never really have a chance to see a couple of decades of dirt roll off at one time. It was really impressive.”

Johnson said the veteran-owned company “jumped at the chance” to offer its services after it was contacted by Lee Phillips, a senior project manager with the Leesburg Department of Plan Review and a member of the county’s sesquicentennial committee.

“We have a love for our vets, and we try to do work in the community that allows them to be honored, and to have the respect that they should have,” Johnson said.

That respect was hard to come by for African American Union soldiers who resettled in Loudoun after the war, Grigsby said. Confederate veterans were hailed as heroes, and even the Loudoun Rangers — the only cavalry unit in Virginia to fight for the Union — has received a great deal of attention over the years.

“But African American soldiers, when they came back, it was a different experience,” Grigsby said. “It was the South, and they were second-class citizens. These men never really got to have that sense of honor, and many of their stories got lost.”

And so the act of tending to their grave sites and sharing their stories with an official marker is especially significant, he said: “Not only does it acknowledge the contributions of the people who are there, but it’s like a very delayed tribute to them.”