Students use X-ray imaging to study Blackbeard's booty
08/24/2014 8:00 PM
08/25/2014 5:10 AM
Students in Davidson College’s physics department have been examining artifacts from a long-ago grounded ship off the North Carolina coast that state officials say was Blackbeard’s Queen Anne’s Revenge. But this isn’t a treasure hunt.
For them, the prize is in the discovery – uncovering clues about life in the early 1700s, perhaps even solidifying evidence that these are indeed pieces from Blackbeard’s ship – and in the chance to gain and share knowledge in many fields based on what they’ve learned from new technology.
Their quest revolves around new software that creates a three-dimensional image of an object, enabling views from different angles. Davidson physics professor Dan Boye says the nondestructive X-ray imaging system, created by the Digitome Corp., has applications that aren’t limited to science; the technology can be used for topics of interest in the humanities and social sciences.
Of course, using this kind of equipment to examine artifacts from a sunken ship is “a different kind of exciting,” he said.
The 3-D advantage
When the Intersal company discovered a shipwreck in 1996, many speculated it was the Queen Anne’s Revenge due to its sheer size and weaponry found in the rubble. In 2011, mounting evidence in the form of recovered pieces prompted the N.C. Department of Cultural Resources to confirm the wreck as the Blackbeard ship. Despite the absence of irrefutable proof, this is generally accepted.
Some objects are embedded in what’s known as a concretion – a solid, rock-like blob formed by the accumulation of matter, especially within the body or mass of sediment. Often a composite of small concretions builds, layer upon layer, around a small nucleus.
“The big part of a concretion is where the iron or the silver or any of the other metals were, and the smaller parts that come off it are organic,” Boye said. “This ship sank, and it had several decks that crumbled in on each other, and so these decks and other materials were made out of wood – but there was also iron there, so you get sort of a pile of mixed materials. Depending on what kinds of materials those are, a concretion forms in different ways.”
These concretions can be a barrier to discovery when using two-dimensional imaging techniques. Ryan Kozlowski, a Davidson physics major and one of the Digitome student operators, said the technology helps remove these obstacles.
“One concretion may have lead shot, the remnants of an iron nail and a silver coin, but a 2-D radiograph cannot provide ample spatial information to reveal the arrangement of these objects relative to one another in the concretion,” he said. “Further, an individual object may be at an angle that prevents simple 2-D imaging, or may be too complex to understand from a 2-D image alone. A Digitome 3-D exam of a concretion can overcome these challenges and possibly reveal previously unnoticed objects.”
Here’s how it works: The Digitome software creates a 3-D space, occupied by “voxels” – 3-D pixels. The shape, size and intensity of each voxel are determined from multiple 2-D radiographs taken from up to 32 different perspectives. The entire object or region of interest appears in each radiograph.
Unlike a CT scan or computed tomography, the system isn’t limited to one configuration. The software instantly assembles the different views so any 2-D mathematically defined contour can be viewed.
The system is also portable, which is ideal for remote locations. The mounting fixture and image plate are removable.
Working at the Queen Anne’s Revenge Conservation Laboratory, a part of the N.C. Department of Cultural Resources located at East Carolina University, Boye said students have examined about a dozen objects. The highlights have been two coins.
He said members of the conservation lab initially weren’t sure they were coins. “A silver coin that’s been in the ocean for that length of time has no pure silver left,” Boye said. “It rusts. It’s silver oxide at this point.
“With the two-dimensional X-ray, they can tell the density of the object relative to X-rays. So they know it’s made out of silver; it has sort of the right shape. The faces that you see on the X-ray are a composite of the two faces – the top face and the bottom face.
“With it having been oxidized, it’s hard to tell exactly what it is. It’s also not in a nice, flat concretion. It’s in a concretion that has two sides to it, but when you lay it down on the table, it will rock back and forth.
“But when we take our (3-D) exams, we’re able to separate the top face from the bottom face. By doing that, we’re able to show that one of the objects that they thought was a coin was indeed a coin from the period of other coins that were found at the sunken ship.”
Another object was found to be a coin, based on the faces revealed from 3-D imaging.
Boye said that with the 3-D technology, “We learned a lot about the times, the culture, the way things were done, the way things were made. For instance, this coin idea is interesting from a material science standpoint because one of these coins is very similar to ones they found that were made at the Mexico City mint. A coin person looked at this and said it was a “fleet real” silver coin from the period from 1714 to 1718.
“We were able to look at a tool that’s very similar to what we would consider today to be a file or a prying tool, a sanding tool. It had some extra stuff in it that showed these guys were pretty clever about modifying their tools. You start thinking about these objects the way they thought about them and how they were going to apply them.”
Boye emphasized that his team members aren’t experts on underwater archaeology. “We work with the people at the Queen Anne’s Revenge conservation lab, and we were able to show them things and they would say, ‘Oh, that’s what that is.’ Or they educated us about the coins and how coins and metal will essentially oxidize – rust – and organic materials won’t.”
The students have also examined objects from the Davidson art department (see http://digitome.davidson.edu) and Davidson library, where an examination of a brittle prayer pouch showed a scroll inside without opening it. They’ve collaborated with faculty and students in the biology department, and a faculty member in the anthropology department.
“This would be called applied physics,” Boye said. “We could walk in with a hammer, drive in the nail and then leave. For us, that’s not the way we want to treat this. Our students are plugged into the actual project. They want to know about what it is they’re applying this thing to do.”
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