ノース・キャロライナ州の沈没船ー保存処理

2009年冬にノースキャロライナ州の海岸で船の一部が海岸発見されたニュースは以前お伝えしました。この船は約400年前のものだそうです。発見地点周辺では昔から16世紀ごろの遺物がよく見つかることが知られていたそうですが、たまたま嵐などにより埋まっていた船の一部が露出し、発見に至った模様。この船の全長は１１０フィートほどだとか。

現在、この船の保存方法が検討されているそうですが、なかなかどの方法をとるか決まらないそうですが、その間に木材の劣化が進んでいるようです。木材の保存にはいろいろな方法がありますが、果たしてどの方法がいいのか？ポリエチレングレコールを使うのが一般的ですが、すでに乾燥している木材をまた液体につけるのは劣化や変形を促すことになりかねません。瞬間凍結法もありますが、大きな部材は不向きです。バラバラにして一部材づつの保存になるのでしょうか？また、シリコンオイルを使うことも出来ますが、費用が掛かることと、再処理できないことなどが問題視されています…なにやら難しい話ですが、専門家が決められないでいる間に木材がどんどん劣化しているのは事実です。

個人的には保存処理のプランを立てるまで発掘をしないのが鉄則ですが、このようにたまたま発見された場合はそうもいえません。適切な保存方法を考え出し、充分な予算が立てられるまで埋め戻すことも可能でしょうか？まだまだ完璧ではない保存処理。水中考古学者にとって重要な課題です。

The Virginian-Pilotから引用

After enduring some 400 years buried beneath the Corolla surf, the oldest shipwreck yet found in North Carolina sits on concrete drying and cracking in the Outer Banks elements.

Experts are scrambling to figure out how best to save it: Submerge it in regular baths, soak it for years in a substance also used in antifreeze, coat it in sugar water, saturate it with an expensive silicone oil or freeze-dry it. Or maybe some combination.

“I’m not going to get a second chance on this,” said Joe Schwarzer, director of the Graveyard of the Atlantic Museum and the state’s maritime museums. “I’ve got to do it right the first time. If we fail, I’d like to know it was an informed failure.”

Advice is coming from several sources, including scientists working on remains of the Queen Anne’s Revenge that Blackbeard commanded and the Civil War-era warship Monitor.

Experts at East Carolina University are investigating the wreck in Corolla to determine what ship it was and how best to preserve it.

Eric Nordgren, a conservator with the Mariners’ Museum in Newport News, plans to learn more about protecting ancient waterlogged wood while on a trip to England.

“It takes a lot of time and resources to preserve a shipwreck,” Nordgren said, adding that funding is limited.

It may be that the 12-ton remains of the shipwreck might be better off outside, sitting on a concrete apron just outside the museum’s back door, Schwarzer said.

Schwarzer said he is using one short, thick beam to see which is better: indoor or outdoor storage. So far, the beam inside a climate-controlled room also shows signs of deterioration, he said.

In November and December 2009, storms uncovered most of the wreck on the beach not far from the Currituck Beach Lighthouse.

For years, beach combers Ray Midgett and Roger Harris had been using a metal detector around parts of the wreck sticking up from the sand. They found old coins from the early 1600s and other artifacts.

But once the wreck was exposed, the surf pounded it and carried it down the beach and back, breaking off parts.

Alarmed, Midgett began writing letters asking for help. With backing from state Sen. Marc Basnight, members of the Wildlife Resources Commission and volunteers used heavy equipment to drag the wreck to a lot near the lighthouse. In July, the wreck was moved to Hatteras.

“It’s very difficult, which is why we seldom recommend removing these things from the beach,” said Nathan Henry, lead conservator with the North Carolina Underwater Archaeology Branch.

Henry recommended getting the entire 17-foot by 37-foot remains indoors.

But he acknowledged, “You could debate this all day.”

For instance, a shipwreck on display in the Town of Nags Head has been in the elements for more than 30 years without extensive deterioration. But in a humid climate, insects and mildew can take a toll, Henry said.

A long-term soaking in polyethylene glycol, known as PEG, may be the best technique available to preserve shipwreck lumber, Henry said.

Parts of the Queen Anne’s Revenge soak in large vats of PEG solution. Ideally, pieces brought out of the water are quickly submerged before they dry out. The technique would not be as effective with the Corolla shipwreck because it has already dried and cracked, he said.

PEG, a chemical used in a wide variety of products, including antifreeze and medicine, replaces the water in the soaked wood. It comes in a variety of forms from liquid to powder. Typically, the solution used for shipwrecks has the consistency of warm syrup, Nordgren said.

A shipwreck known as the Vasa in Sweden was sprayed with polyethelene glycol for many years. Later, curators discovered the presence of sulfuric acid within the wood that could cause deterioration. Experts are not certain how much PEG had to do with the formation of the acid, Nordgren said.

Ancient canoes saved from Lake Phelps in Washington County were soaked in a sugar water solution and have held up so far. There are some concerns, however, that in the wrong environment, sugar water could attract bacteria or insects, Nordgren said.

Some parts of old ships have been freeze-dried, but they should be treated first with PEG, Henry said. The trick is finding a freeze-drying machine large enough to handle the Corolla wreck, Nordgren said.

Silicone oil is one of the latest techniques developed for preserving wrecks, but treatments are typically used for small parts due to the cost. The silicone oil treatment, however, is irreversible, Nordgren said, and conservators would rather not use a treatment that is irreversible, since something better may come out later.

“If it doesn’t work, you’re out of luck,” he said.

Some wreck remains are bathed in fresh water to remove salt, Nordgren said. In that technique, the bath water should be changed regularly or the salt can crystallize and cause the wood to crumble.

Experts, with the aid of computer models, calculated that the ship found in Corolla was 110 feet long by 20 to 30 feet wide. It was broad and slower-moving and most likely used for hauling merchandise, Schwarzer said. Its 12-inch by 12-inch beams were made from European white oak, he said.

The wreck dates from the early to mid-1600s, making it the oldest among the hundreds of shipwrecks found on the North Carolina coast.

“If this ship were carrying a full load of cargo, it would have been a devastating loss to whoever was funding the ship,” Schwarzer said.

And now, Schwarzer and others are trying to make sure it isn’t lost again.

Jeff Hampton, (252) 338-0159, jeff.hampton@pilotonline.com

引用元：http://hamptonroads.com/2011/01/experts-race-clock-preserve-nc-shipwreck