Because removing the shells would damage the fragile walls of the aging fort in Charleston Harbor, they have been preserved in place by scientists from the nearby Clemson University Restoration Institute.
The project not only helps preserve the shells and the wall, but allows visitors to better imagine what it might have been like for the Confederate defenders of the fort in Charleston Harbor. Historians say the city and the fort were the object of the longest bombardment in the history of the Western Hemisphere.
One day earlier this month, institute conservators Liisa Nasanen and Paul Mardikian worked on the shells, first applying deionized water to them and then carefully catching the runoff to test how much salt has been removed from the iron.
The salts remaining can continue to corrode the iron which is exposed to the open salt air.
"It would be great to remove all the salts," Mardikian explained. "But all we are doing now is reducing the threshold. We're reducing the amount, but can't say we are removing all the salts."
Then the shells were dried, using a device similar to a hair dryer, before a material was applied to help consolidate the iron on the shell so no more metal flakes off.
Nasanen is heading the project and has worked with Clemson researchers to preserve shells found at Sumter and Fort Moultrie with subcritical and supercritical treatment in the lab. She said that trying to conserve iron objects outside is not ideal.
"It's always something we have to battle with outdoor projects," she said. "We have to look at the humidity and the temperature and things like that. We have to not only look at the artifact itself but the conservation materials to make sure they work."
In subcritical technology, water under intense heat and pressure has unique dissolving characteristics. In this case, items are put in a reactor vessel, and salts that can cause deterioration are quickly removed. In supercritical technology, carbon dioxide subjected to intense heat and pressure and has been used to remove moisture and preserve items including cork from shipwrecks.
Working outside is different, Nasanen said.
"It's going to be a continuous monitoring protocol over the next several years," she said, adding the current state of the shells has been documented using computer technology. "We want to see over the next several years if our work has done any good for the artifacts."
The work is being done under a multi-year, $900,000 agreement between the National Park Service and Clemson, said Rick Dorrance, the chief of resource management at the Fort Sumter National Monument.
Under the agreement, Clemson scientists are working with the National Park Service to research the best ways to preserve both the artifacts and the architectural elements of both Fort Sumter and Fort Moultrie on nearby Sullivans Island, he said.