X-radiography in Archaeology: A M1841 “Mississippi” Rifle Case Study
As the science of archaeology has progressed, new and innovative technologies and analyses have been applied to provide greater understanding and deeper interpretations of the features and objects recovered in our investigations. One of the oldest technologies applied to the study of artifacts is radiography. Only one year after its discovery by Wilhelm Röntgen, x-radiography was used to investigate a Ptolemaic mummy bundle in 1896, and the advantages in non-destructive testing were realized. For over 100 years, archaeologists have continued to use x-radiography to investigate artifacts.
X-radiography is most often used in the examination of metal artifacts, particularly for those objects that are obscured by concretion or corrosion products. These images can be very useful in the identification of artifacts, but the x-ray data can have multiple applications. Determining the object type can lend itself for a more complete record and interpretation of the context where the object was recovered. It also impacts the long-term preservation of the recovered materials. Curators and conservators assess not only the significance of an object but how it may be used in the future for research or display, and how its physical condition may impact these uses. Long-term care of collections has an associated cost, so collections managers use all of the information available to make the best use of curation and conservation resources. X-ray images can reveal the degree of deterioration and help determine if an artifact needs conservation, can survive treatment without damage, or if the x-ray alone can provide the necessary documentation without additional intervention. If conservation is required, the images can inform conservators how to best proceed in the treatment of that object.
A Civil War rifle (Figure 1) is currently in the beginning stages of conservation treatment at the Maryland Archaeological Conservation Laboratory (MAC Lab). It is a M1841 Mississippi Rifle used by both Union and Confederate troops, recovered from the site of the 1st Battle of Bull Run in Manassas, VA. Preserved in the wet, dense-packed clay of the creek bed, the wood stock is waterlogged but well preserved and must undergo specialized chemical and drying treatments to prevent its cracking and warping. Before any treatment can begin, certain safety measures must be taken, namely determining whether the firearm remains loaded. X-radiography is the perfect tool to make that determination. Because a lead projectile is a denser material than the surrounding iron barrel, the lead appears brighter on the x-ray image. The presence of a bullet and a preserved powder charge requires that conservators first drill out the charge to neutralize the hazard. The x-ray image can provide precise details to locate the best area to drill while minimizing damage to the object.
Figure 1. 1841 “Mississippi” Rifle, before conservation treatment with associated copper alloy hardware (trigger guard, butt plate, and hinged patch box lid). Photo courtesy of the Winery at Bull Run.
In the case of this rifle, a Minie ball and preserved powder charge were identified in the x-ray images (Figure 2). Using the x-ray image, the diameter of the Minie ball was measured and determined to be .54 caliber. The caliber of the Minie ball can be used to date the rifle as the M1841 was originally produced in a .54 caliber but was later modified to a larger caliber so that it could use the new standard .58 caliber Minie ball rounds. The images also reveal a broken main spring, which may have been the reason this firearm was discarded during the hasty retreat of Union soldiers during the battle. Another interesting find revealed by the x-ray images is the presence of a spare nipple in the patch box located on the stock that would have also held tools for maintenance and repair.
Figure 2. X-radiographs of the rifle lock showing the three groove Minie ball, broken main spring (top), and extra nipple (bottom).
As conservators move forward with the treatment of this artifact, the x-ray images will provide a guide during the cleaning process to denote where the iron has been replaced with fragile corrosion products reveal surface details.
With the widespread accessibility and affordability of digital X-radiography, archaeologists should continue to employ this technology to document and study artifacts. People who do not have access to an archaeological facility with x-radiography might be surprised how many x-ray technicians in other fields (universities, hospitals, large animal veterinarians, or dentists) may be enthusiastic about archaeology and willing to offer help.