Page 234 - Copper and Bronze in Art: Corrosion, Colorants, Getty Museum Conservation, By David Scott

P L A T E 79 Bronze mirror, Eastern Han dynasty (25 -
220 C E . ) , D I A M : 14.3 cm. The back of this mirror shows
typical black patina, consisting primarily of copper
oxides and tin oxides. Here both the alpha+delta eutec-
toid phase and the alpha phase of the bronze have cor­
roded. Freer Gallery of Art, Smithsonian Institution
(F1937.30).
P L A T E 8 0 Photomicrographs of cross sections of patina
A
samples from two Chinese mirrors: , a mirror from the
Warring States period (475-22 1 B . C . E . ) , showing a green
patina with preservation of the copper corrosion products
and uncorroded alpha+delta eutectoid phase to the
outer regions of the corrosion crust; and , B a mirror
from the Han dynasty, with a black patina in which the
alpha+delta eutectoid phase as well as the copper-rich
phase have corroded (both at magnification x488).

P L A T E 81 Statuette of a Cat, Egyptian late period (700 -
30 0 B . C . E . ) . Bronze, H : 24.2 cm. This bronze casting was
conserved by patina-removal techniques that were com­
monly in use from around 1890 to 1970. The entire patina
has been stripped away by the chemical or electrolytic 81
treatment. Most objects treated in this manner have oxi­
dized metallic surfaces of a similarly raw appearance and
are now usually confined to storage vaults. Ashmolean
Museum, Oxford (1962.608).

217