Individually, fourree coins and brockages are rather common. This denarius of Hadrian is unusual in that it combines both of these 'varieties'. I have seen one other example of this combination (a Republican denarius).
The inset magnification of a small area from the reverse shows a pit in the silver that passes through a (white in the photo) region of silver copper alloy which bonds the relatively pure silver on the surface to the copper core. This alloy, the 'eutechtic', is the mixture of 72% silver and 28% copper and has the lowest melting point of any combination of these two metals. This material is used as silver solder. Fourrees were produced by wrapping the copper core with silver foil. This sandwich was heated and struck with dies. If the heating and the force of striking were sufficient the two layers would adhere producing a thin layer of eutechtic at the bond. Some workshops strengthened this bond with a powdered eutechtic sprinkled between the layers. It is not always easy to tell which method was used on any particular coin but the thickness seen in this photo suggests that this coin was produced with this 'added eutechtic' technique.
For more technical information on fourree production techniques see: Campbell, William, _Greek and Roman Plated Coins_ Numismatic Notes and Monographs No. 57, American Numismatic Society, 1933.
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© 1997 Doug Smith