What's in a Lead Ball? Using X-Ray Fluorescence to Read 18th-Century Ammunition

The problem with round balls

In eighteenth- and early nineteenth-century America, small-arms ammunition was simple: round balls of soft metal, mostly lead, sometimes with other metals such as pewter or silver mixed in. The guns that fired them were anything but uniform — pistols, rifles, trade guns, carbines, fowlers and big-bore wall guns, of American, French, Spanish and English make — and varied from one military unit to the next.

That leaves archaeologists with a puzzle. Unlike Civil War bullets, these balls carry few clues about who owned them. Diameter (caliber) and weight hint at the weapon, but much remains unknown, and a ball that was fired and badly flattened can be unrecognizable. Looking at bullets by eye alone limits what a battlefield can tell us.

Adding chemistry

Researchers Daniel T. Elliott and Michael Seibert of the LAMAR Institute propose a standard way to analyze lead balls that combines the traditional record with elemental analysis by portable X-ray fluorescence (pXRF).

Two workshops

• December 2015. Using a handheld Bruker Tracer III, Elliott sampled several hundred balls from Revolutionary War battlefields in Georgia and South Carolina, from colonial and early federal forts in Georgia, and from Native American village sites in Georgia. Physicist Bruce Kaiser, analyzing the data, found significant elemental differences between assemblages. The work also showed pXRF works well on old museum collections.
• June 29–30, 2017. A larger workshop, Get the Lead Out, funded by a 2016 grant from the NPS National Center for Preservation Technology and Training and held at the Coastal Georgia Center in Savannah, brought archaeologists, museum curators and physicists together to test samples from their own sites and collections, guided by physicists expert in pXRF. Its results seed a growing database of the elemental makeup of early ammunition.

The findings also draw on elemental data researchers have gathered since 2012.

Open questions

The differences are real; what they mean is still debated. Was tin or antimony added on purpose, to make balls fly better — or simply because good lead was scarce? Are non-lead additives tied to particular armies or weapons?

The team admits its early hopes were high, "albeit naïve," as they put it: they had hoped pXRF could trace lead to its source. That job is better done by isotope analysis, which pXRF doesn't provide. Still, combined with isotope studies and data from lead ore sources, pXRF results could build baselines for comparing battlefield assemblages and feed a global dataset — helping show how military supplies were distributed and how strategy played out, from the world scale down to a single battlefield.

Sources

Based on "Get the Lead Out: Towards Identifying Ammunition on Eighteenth- and Early Nineteenth-Century Battlefields and Settlements," by Daniel T. Elliott and Michael Seibert, The LAMAR Institute, Savannah, Georgia, 2017 (LAMAR Institute Publication Series, Report 205; NCPTT grant P16AP00371), as posted by the National Park Service. Workshop photographs without a credit are left out; rewritten in hubnx's own words.