Walnut shells are more gentle on the historic emblems than sandblasting, they explain.
"I figured it would be labor-intensive," said Tom Rostkowski of Middle River, Pa., a member of the all-volunteer Maryland Monument Commission.
The commission, appointed by the governor to protect these historical markers, came to Antietam Tuesday to observe the restoration techniques.
It has been nearly 10 years since the bronze plaques on the turn-of-the-century Maryland Monument were restored by the commission.
That and other monuments are once again showing the damaging effects of the weather. Some of the bronze has faded to green, a sign of corrosion.
"The weather really attacks them," Rostkowski said.
The commission has identified 300 monuments throughout the state, including 33 in Washington County.
So far, 70 monuments statewide have been cleaned and restored using public and private money.
Since 1995, when Parris Glendening was elected governor, the commission has received $40,000 to $50,000 a year from the state, said Secretary of State John T. Willis.
The work of the commission has compelled the park service to continue the upkeep of monuments at Antietam, said Willis, who chairs the commission.
"By us coming here 10 years ago, we kind of shamed the federal government into doing something," he said.
The park service works on monument maintenance from June through September, said Kemble, cultural resource management specialist.
It takes more than a week to clean and wax an all-bronze statue. Ideally, a statue should be waxed every five years.
But there are eight monuments at the park that have deteriorated more quickly because their bronze faces are nearly horizontal and exposed to the elements.
The park service and the Maryland Historical Trust have teamed up to test some lacquers on those monuments to see if they hold up better than they did with waxing, which lasted only about a year.
Waxing is the preferred method because it's easy to maintain and renew. Lacquer has to be removed and reapplied, said Nancy Kurtz, monuments survey administrator.