The Roman period Crosby Garrett helmet, which I was lucky enough to do some superficial analysis on in 2010, will be part of the Royal Academy’s Bronze exhibition which runs until the 9th of December 2012.
The RA have used the title of the exhibition – Bronze – to refer to any object made of a copper alloy. Metallurgically the word tends to refer to a specific alloy of copper and tin, but is traditionally used in museums and galleries to describe any copper alloy object. It can be difficult to tell if an historical object is actually made from bronze or another copper alloy, such as brass (copper and zinc) or gunmetal (copper, tin and zinc) anyway, so it makes a convenient short-hand.
My analysis, although unfortunately only qualitative, suggests that the majority of the helmet isn’t made of bronze in the technical sense, but of a gunmetal which may have had some lead added to it. This is a common enough alloy for an object of this period, when it seems the Romans were very flexible about the metals the used even for time-consuming and beautiful objects like the helmet.
I haven’t heard much about the helmet since it was sold at auction for more than two million pounds, however since it’s in private hands now it’s hard to say when there’ll be another chance for the public to see it. Well worth a look if you’re in London, that’s for sure.