X-ray Imaging of Archaeological Artifacts at the Madison Accelerator Laboratory

Principal Investigator:
Dr. Harold Butner, Professor, Department of Physics and Astronomy/JMU

Co-Principal Investigator:
Dr. Tilda Pendleton, MAL Laboratory Manager

External Collaborators:
Chelsea Blake, Conservator/Project Manager (formerly Betsy, currently Skiffes Creek),, Virginia Department of Historic Resources
Laura Galke, Chief Curator, Virginia Department of Historic Resources
Dr. Elizabeth Moore, State Archaeologist, Virginia Department of Historic Resources
Katherine Ridgway, State Archaeological Conservator, Virginia Department of Historic Resources
Leslie Straub, Collections Manager, Virginia Department of Historic Resources

Grapeshot From the Revolutionary War Period Vessel Betsy

As an example of how the Madison Accelerator Laboratory can help museums in their mission to understand and conserve their exhibits, consider what X-rays reveal about an artifact recovered from a vessel (Betsy) which was involved in the battle of Yorktown during the Revolutionary War. Betsy was not a warship, but instead was a collier (a ship used to transfer coal from Britain). During the battle of Yorktown, it was scuttled (or sunk deliberately) to try and protect the British
in Yorktown from French naval guns. The Virginia Department of Historical Resources (DHR) recovered about 50% of the ship’s contents in the early 1980s, and treated the artifacts to conserve the water-logged materials.

More recently, as new techniques have become available, DHR has been undertaking a major re-treatment conservation project of Betsy with support from a Maritime Heritage grant from the National Park Service. Conservation of Betsy is part of the DHR’s commitment to foster, encourage, and support the stewardship of Virginia’s significant historic, architectural, archaeological, and cultural resources.

What is involved when you want to conserve artifacts – particularly those that are recovered from underwater – is detailed at the DHR’s website about conservation of Betsy.
https://www.dhr.virginia.gov/spotlight-on-dhr-collections/spotlight-on-the-dhr-conservation-lab/

A Grapeshot Shell from Betsy

Grapeshot shells consist of iron balls, wrapped in textile, and secured by rope, as shown in this illustration from the same time period (18th century).

        Excerpt from Grapeshot Treatise (public domain)

One of the artifacts recovered from Betsy was a grapeshot shell, shown below.

Courtesy of Virginia Department of Historical Resources (https://www.dhr.virginia.gov/)

You can see two of the iron balls that make up the grapeshot are exposed in the first figure, but the rest of the grapeshot shell is covered in concretion, a mixture of corrosion, mud, shell, and other materials.

While it would seem “easy” to remove the mud, the goal of historical conservation is to not only to expose the object, but also to preserve as much as possible of the artifact without damaging the integrity of the object as a whole. This means that more time and care must be used – so not only the iron balls, but other parts (wood, textiles, rope) of the grapeshot shell are preserved as much as possible.

Role of X-ray Imaging

As you can see, the grapeshot is covered in concretion that has hardened over time. Before going further with the conservation process, the conservators at DHR wanted to get a better look at the interior through X-rays. Here is where the MAL X-ray imager can help.

X-rays at 140 kV can penetrate the mud, revealing underlying details of the wood, textiles, rope and metal contained within the mud (conglomerate) covering.

Courtesy of Virginia Department of Historical Resources (https://www.dhr.virginia.gov/) and Madison Accelerator Laboratory

The X-ray images reveal the interior structure of the grapeshot, letting conservators know exactly where the iron and wooden parts of the shell are located.

Some features revealed by the X-ray images include:

• The wooden base of the shell, with the wood grain visible
• A central hole in the wooden base, where the wooden dowel could be inserted
• Four rows of 5 iron shells, each about 1.3 inches in diameter
• A wooden dowel cap at the top, also seen in the lower left of the 18th century illustration

Visual and X-ray Images of the Grapeshot Shown Side-by-Side