Discovering What Lies Beneath

Hey Fort Followers,

        We’re back here in the lab at Western Michigan University, and the work we started this summer continues with further curation and research. Our collection from this summer includes a number of objects made of metal: lead musket balls, copper tinkling cones, and loads of iron artifacts whose functions aren't always so obvious. At our site, an iron artifact can often come out of the soil in a much larger lump of corroded iron and soil which blankets the entire object. As much of this corrosion as possible needs to be removed during curation in order to study and analyze these objects more effectively.

The corrosion presents a real challenge in its resistance to removal, the work we do to remove this corrosion involves using very fine metal implements to slowly work off flakes and crumbs of oxidized iron and soil until the artifact’s original surface is revealed, often much darker and smoother than the corroded reddish concretion surrounding it. The work is painstaking and slow, because the metal underneath has often been leached from the surface, leaving behind a much more fragile and porous substrate which can break away with too much force. When corrosion invades the object, the corroded material can expand and cause “corrosion jacking” which splinters the object distorting its original shape (Turner-Walker 2008).

Many of the iron objects recovered this season proved to be nails, which were hand-wrought throughout the entire occupation; later machined nails wouldn’t see regular use until the late eighteenth century (Wells 1998). Pictured here is the removal of a nail from its surrounding concreted iron oxide. The nail underneath proved to be relatively intact and had only one area where corrosion invaded the surface so thoroughly that further cleaning with mechanical tools was too risky. Other tools, such as compressed air with abrasives, vibrating picks, or chemical solvents could be used if the artifact was to be examined more thoroughly (Turner-Walker, 2008).

The next image is an unidentified iron object undergoing cleaning with a dental pick. The object starts as an amorphous lump of corroded soil, which is slowly picked away to reveal an exciting find. It’s a pintle! The corrosion had enveloped the entire outer surface but didn’t fully ingress into its cylindrical knuckle. I used a delicate swirling motion to drill away until the dental pick entered the empty space inside, and slowly worked the opening up by twisting the angled end of the pick until the entire opening was exposed. 

After an iron object has been cleaned, it can be entered into the catalog, now that an accurate weight can be taken, and the type of artifact can be more precisely defined. As with all metal artifacts, halting the oxidation and corrosion is the primary concern, so each is stored with a desiccant, such as silica gel, to prevent further degradation. These are then sealed with their tags in plastic bags, where future researchers can retrieve them.

Curation presents all sorts of cool opportunities to spend time with each individual artifact, and I’ve found this to be one of my favorites, as it’s evocative of the careful methodical work of paleontologists, and even like its own sort of excavation in the lab. I’m really excited to keep working on these types of projects and seeing what our team can learn from these surprisingly delicate pieces of the Fort.

-Jacob

References:

Turner-Walker, G. (2008). A practical guide to the care and Conservation of Metals. Wang Show-Lai.

Wells, T. (1998). Nail Chronology: The Use of Technologically Derived Features. Historical Archaeology, 32(2), 78–99. https://doi.org/10.1007/bf03374252