 |
Commenting on
the Riverside lump, R666, on left, Neiburger said
"Xeroradiographic analysis, with its excellent
capability for identifying voids in the metal (edge
enhancment) shows many characteristic casting bubbles:
typical of melted copper. These voids, upon stereo- microscopic examination, are empty and do not contain silica or other inclusions. The rounded voids do not appear in natural float copper and could only have been caused by melting. Microscopic analysis of the crystal structure show oxide inclusions (black accumulations) on the grain boundaries. This occurs only in castings." The Riverside lump is unlikely to be an intrusion from the historic period, Neiburger said, because it was found 104 cm below the surface in association with other copper artifacts with "similar corrosion patterns, patina thicknesses and colors," Neiburger said. |