ROMARCHITE AND THE CORROSION OF PEWTER ARTIFACTS

Pewter, a tin-rich alloy, has been widely used for ornamental and utilitarian purposes for more than 2000 years. Pewter was found to be durable, relatively easily worked, resistant to corrosion, and to resemble silver in appearance. The broad use of pewter and its resistance to weathering provide a rich legacy of archeological materials recovered from different geological environments. Pewter plates and implements have been recovered and examined from what is believed to be the wreck site of the Queen Anne's Revenge, the flagship of Blackbeard the pirate, near Beaufort, North Carolina. The reaction of pewter with seawater has resulted in the formation of several corrosion minerals. These minerals have generally been assumed to be cassiterite and/or abhurite. This study has confirmed the presence of romarchite, SnO, a little known mineral, as a significant phase in most of the corroded pewter artifacts from the wreck site. The romarchite commonly occurs as laths up to 100 microns in length and has formed in association with abhurite, Sn3O(OH)2Cl2, and hydroromarchite, 5SnO.2H2O. Electron microprobe analysis of the pewter indicates that many artifacts have significant amounts of copper as an alloying metal; romarchite has been found on both Cu-rich and Cu-poor pewter. Observation and identification of romarchite will be useful in understanding the stability of pewter when left to the weathering environment and the nature of pewter corrosion products.