Cyril Stanley Smith's 1976 Metallurgical Report on
"Francis Drake's Brass Plate"
Detail of placque.
Photograph reproduced courtesy of the
Lawrence Berkeley Laboratory.
Sir Francis Drake skirted the coast of California while "encompassing" (circumnavigating) the globe in his flagship, The Golden Hinde, between 1577 and 1580. According to a journal kept by the ship's chaplain, Francis Fletcher, the company "fell with a conuenient and fit harborough" (put into a convenient and suitable harbor) for refitting in June 1579, a task requiring about one month. While in the harbor Drake received throngs of Native Americans, claimed California on behalf of Queen Elizabeth I, and caused a brass plaque to be made and erected on a wooden post as a token of his discovery and conquest. A small hole chiseled in the plaque, or plate, accommodated a silver sixpence bearing the Queen's portrait. In 1936 a young Californian found a crudely lettered brass plaque partially buried on a ridge overlooking San Francisco Bay, which history buffs and civic boosters were eager to accept as a genuine relic of Drake's visit. Others were skeptical, but a metallurgical analysis performed by C. G. Fink and E. P. Poluskin (published by the California Historical Society in 1938) supported claims of authenticity and "Drake's Brass Plate" became a prominent exhibit at the Bancroft Library, University of California, Berkeley. In 1976, at the request of the Bancroft's James D. Hart, MIT metallurgist Cyril Stanley Smith subjected the artifact to a binocular microscopic examination and submitted the report reproduced here.
Radiograph of "Drake's Brass Plate." Reproduced courtesy of the Lawrence Berkeley Laboratory.
Smith studied the composition, microstructure, directionality, and other characteristics of the plate. His examination suggested that the brass was rolled flat, not hammered flat, and that its edges had been sheared instead of being chiseled. Elizabethan smiths would have used a hammer and chisel to shape the plate. He found that the composition of the brass had an unusually high zinc content for the 16th century. His analysis revealed a number of other anomalies, including a superficial patina and surface corrosion that was surprisingly uniform, given the assumption that the plate had been buried for centuries in soil that contained variations in roughness and porosity. Smith noted that environmental variations should produce large differences in corrosive attack over time, and he was "inclined to the opinion that the plate is a modern forgery." He added, however, a caveat: "I firmly believe that evidence from the viewpoint of a material scientist should not be taken as firm evidence of the modernity of the plate unless and until the same criteria have been applied . . . to ancient material of undoubted provenance." He was careful to distinguish between scientific questions and historical questions, "though science, of course, aids in the historical decision." Evidence from other disciplines seemed to corroborate the metallurgical analysis. Some scholars, for example, questioned the authenticity of the spelling and style of lettering. It now seems unlikely that the plaque could have been produced before the late 19th century.
Smith's April 27, 1976, report to James Hart, originally marked "CONFIDENTIAL," was subsequently made public by the Bancroft Library. Hart issued a pamphlet summarizing Smith's results and additional tests conducted at the Lawrence Berkeley Laboratory (University of California) and the Research Laboratory for Archaeology and the History of Art (Oxford University). The plaque is owned by the Bancroft Library.
The Cyril Stanley Smith Papers (MC 254), containing files about metallurgical analysis and other topics, are available for use in the MIT Institute Archives and Special Collections.
Object of the Month: November 2001