An advance in iron preservation aids conservators

Work on Civil War submarine leads to pioneering technique



Research on the H.L. Hunley—a submarine which sunk after successfully sinking a Union warship during the American Civil War—has led to a potentially revolutionary method in the preservation of iron artefacts. Six years of experiments using subcritical (super pressurised) alkaline solutions at the Clemson University Conservation Center at the Warren Lasch Laboratory in North Charleston, South Carolina, has led to a safer and faster way to stabilise iron objects retrieved from the sea and earth.

The treatment of iron artefacts has always been a problem for archaeologists, conservators and curators. Head conservator Paul Mardikian says: “Iron doesn’t like to be iron—it would like to be something else,” adding, “it has a tendency to revert back to its naturally occurring condition which is basically as an oxide.” Salts in the ground and ocean react with iron, causing accelerated corrosion. Once these objects are exposed to the atmosphere, they rapidly deteriorate. “Sometimes all you are left with is a pile of dust tagged with an inventory number,” says Mardikian.

In 2004, Mardikian and his team began treating iron rivets from the Hunley in a subcritical reactor which subjects the objects to high levels of pressure. They found that they were able to penetrate the corrosion layers of the rivets in a fraction of the time of traditional methods (other treatments can take up to six months depending upon the size of the object) and, more importantly, without changing the physical nature of the object. Successful results on marine artefacts led the team to experiment on terrestrial artefacts.

The repercussions of this new technique on the fields of archaeology and conservation are potentially revolutionary. Conservation is a time-consuming and expensive practice. The use of a subcritical reactor will allow objects to be treated in batches rather than individually, drastically cutting time and expense.

Another added advantage of this new method is the ability to adjust the treatment to suit the artefact. Because this technique speeds up the treatment process, conservators can better monitor the object’s progress and adjust the level of alkaline solution as needed.

Mardikian warns that the full effects of this new technique will not be known for at least another ten years when artefacts that have undergone this treatment can be examined to see how they hold up. However, he remains “cautiously optimistic” saying: “The possibility of this technology are endless—this is just the Big Bang of this research.”

The team began their research using a small chamber capable of holding only 40 millilitres of liquid. They are currently conducting experiments on the Hunley’s ballast blocks in a 40-litre chamber and are already planning to build a chamber capable of holding 12 cubic metres of liquid to treat a cannon. They also intend to experiment using different copper-based metals such as bronze.

“Metal 2010”, an important international conference on historic metal conservation, will be held in Charleston from 11 to 15 October.