Northover, P. J.; Northover, S. M. and Wilcox, N. J
Copper for the navy.
In: Cultural Heritage meets Science: The Interface, 14 Sep 2011, Portsnouth, UK.
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The history of protecting the hulls of Britain’s wooden warships with copper sheathing and, later, replacing iron bolts with copper to avoid disastrous galvanic corrosion is well documented. Less well known are the nature and properties of the copper used and the details of its processing.
This poster will present the results of the characterisation of finds of bolts and sheathing from the 1790s to the 1840s using tensile and hardness testing, optical microscopy, electron probe microanalysis, and electron backscatter diffraction.
In the 1790s British copper contained a distinctive pattern of arsenic, silver, bismuth and lead impurities, mostly found in the oxide phase as the result of oxidative refining. Tensile and hardness testing show that the copper of the Napoleonic War era was tough, ductile, and consistent in its properties, with bolts being produced with a harder temper as time went on.
Although the supply of copper to the navy was operated by a cartel the production of bolts was carried out by three different companies following three different patents. In using electron backscatter diffraction to supplement hardness testing in assessing the effects of cold rolling on the copper it was discovered that one of the patents produced a distinctive crystallographic texture in the metal, the result of drawing the bar through a die.
Further research using bolts with makers’ stamps will see whether other attributions can be made, something that cannot be done any other way because the copper is otherwise consistent in both composition and microstructure.
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