NORTH CHARLESTON, S.C. - Clemson University scientists have trimmed years from the time-consuming process of conserving historic artifacts ranging from an old ax head to Civil War shot and a ballast block from the Confederate submarine H.L. Hunley.
The process of using subcritical and supercritical treatment of the items could revolutionize the way historic artifacts are conserved. The technique existed only in theory a decade ago.
"In our case, we still have to convince the conservation community that the object is better" after treatment, said Michael Drews, director of the Clemson Conservation Center at the university's Restoration Institute. "Conservators are very conservative. They have seen a lot of used car salesmen."
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.
There is also a small supercritical reactor at the Warren Lasch Conservation Center, where the Hunley is housed.
In that technology, carbon dioxide subjected to intense heat and pressure has been used to remove moisture and preserve cork from shipwrecks, including a 16th-century Basque whaler, said research scientist Stephanie Crette.
The usual way to stabilize iron artifacts is to place them in a chemical bath or use electrolysis to leech out the salts. Drews said the lab is the only one in the world using the subcritical technique on artifacts.
Scientists first experimented with the technique on small metal shavings and bolts from the Hunley, said Nestor Gonzalez-Pereyra, a researcher and conservator key in designing and building the reactors.
Then larger objects were treated, including a ballast block from the Hunley, the first sub in history to sink an enemy warship. It took about 18 months using traditional methods to conserve the other blocks. The one treated using subcritical technology took 10 days.
The newest reactor holds 40 liters and is now being used to conserve a shell from the Fort Sumter National Monument.
Drews said the work with the technology started in 2003 and was considered experimental until two years ago. Some items treated since have come from overseas, and other conservators can evaluate the work.
"We said you send us the artifacts, we will send them back to you for your evaluation. They have no stake in the game except to evaluate," he said.
So far, the feedback has been positive. But researchers will need more time to determine how well the artifacts hold up after being restored, as a couple of years is not enough, Drews said.
The results appear to be uniform if several objects are treated at once. But the biggest benefit is the time savings.
Two years ago, scientists at the lab finished the six-year process of conserving two guns from the famed Confederate naval raider CSS Alabama. Using the subcritical technique, it would have taken two months, he said.
The next step may be to make a chamber large enough to hold one of the massive, 8-ton guns from the Civil War ironclad ship the USS Monitor, Drews said. The ship's guns are currently being restored by conventional means in Virginia.
A reactor of that size would have to be about 420 cubic feet, about the size of 10 refrigerators, and cost about a half-million dollars. One that could treat the Hunley, which conservators plan to conserve with traditional methods, would have to be 10 times that size.
Even if the reactor for the Hunley is built, there would be risks using the method.
Instead of being a solid shot or a bolt, the Hunley is a complex combination of different types of metals, with pipes, a hand crank for providing power and viewports.
"The Hunley is unique. It's like nothing we have ever treated. And we really don't know what would happen," Drews said.
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