On Display: The Southampton Swivel Gun

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CCI Newsletter, No. 32, November 2003

On Display: The Southampton Swivel Gun

by Tara Grant and Charlotte Newton, Senior Conservators, Conservation Processes and Materials Research

In October 2002, a small swivel gun was found during excavation of a ship buried on the beach at Southampton, Ontario, on Lake Huron. It was excavated by a team headed by archaeologist Ken Cassavoy, under a permit issued by the Ontario Ministry of Citizenship and Culture. Historical research, conducted by the archaeologist and marine historians from the area, has led to a tentative identification of the ship as the Weasel, built in Detroit [in present-day Michigan] in 1786, and apparently lost at Southampton in 1798. If identification can be confirmed, this would be the earliest known shipwreck site in the Upper Great Lakes.

The 1.03-m-long cast iron swivel gun, weighing about 90 kg, was covered with a thick encrustation of smooth pebbles, sand, iron corrosion, and iron spikes and nails. The soft, black, porous corrosion was identified as siderite (FeCO₃). Siderite is a stable, non-conducting iron corrosion product formed when iron is buried in a low-oxygen, highly carbonated soil found in limestone areas or shell middens. The cast iron barrel appeared to be in good condition with a significant amount of iron remaining. The wrought iron swivel mount was heavily corroded and unable to move. The bore was blocked with a pebble-based concretion. X-radiography could not determine the cannon's condition or if it was still loaded.

One of the major problems for iron artifacts is contamination with chlorides during burial. Because the salt promotes corrosion, extensive chemical or electrochemical treatment is required to remove the chlorides and stabilize the iron. However, tests of the storage water and corrosion analysis of this gun found no detectable levels of chloride. Treatment was, therefore, a straightforward mechanical removal of the concretion layers using hammers, chisels, and dental tools and brushes. Cleaning the bore revealed that the cannon did not contain a charge. The cleaning produced an even, hard surface with many details still visible including the touch hole and an inscription. Because the cannon was going into a museum environment and the surface was stable, no surface coating was applied.

The swivel gun is currently on display at the Bruce County Museum, Southampton, Ontario.