Researchers from Northwestern University in the USA have recently tried to re-create the copper working techniques of the Cahokia Native Americans, from over 600 years ago. Using discarded fragments of copper from the area of the old copper workshops, they worked out the processes followed.
     Alix Deymier-Black, one of the authors of the study which was published, explains what they did "We cut through some samples of the copper pieces and polished them to look at the grain structures of the copper with a microscope. From the size, shape and features of the grains inside the copper, we determined that the coppersmiths were likely hammering the copper, probably with a heavy rock, then putting the copper in the hot coals of a wood fire for 5-10 minutes to soften it and then repeating the cycle until they had created a thin sheet of copper".
     They also tried to find out if they laminated large sheets of copper but failed, using the technoilogy that had been available at the time, preferring the theory that multiple sheets had been held together with a type of rivet. Another question was answered using simpler techniques, finding that the way they cut their sheets was by repeated bending back and forth until it snapped.

Edited from EurekaAlert!, PhysOrg.com, Science Daily (13 June 2011)