Page 359 - Copper and Bronze in Art: Corrosion, Colorants, Getty Museum Conservation, By David Scott

[I]f this proceeds, the copper is dissolved by carbon dioxide containing waters, so that
finally pure tin oxide remains which combines with various compounds from the soil
[T]he degree of this decomposition depends on the ratio of oxygen and aggressive car­
bon dioxide in the groundwaters. If oxygen is missing the decomposition will be slow,
even in the presence of high amounts of carbon dioxide.... [I] f there is a lot of oxygen, but
little carbon dioxide, then the metal is often oxidized and covered with a carbonate patina.
(Geilmann 1956:210)

TABLE l l . l COMPOSITIONAL ANALYSIS OF A BURIED BRONZE URN
DATING TO THE EARLY IRON ACE

METAL COMPOUNDS PATINA TIN OXIDE TIN OXIDE
(wt %) ANALYSIS ANALYSIS
NO. 1 NO. 2
Cu 83.70 CuO 54.84 9.30 0.78
Sn 11.85 Sn0 2 28.31 56.07 63.20
Sb 0.53 s b 2 o 5 1.91 2.35 2.80
As 0.14 As 2 0 5 0.40 0.78 0.90
Pb 2.98 PbO 0.27 0.20 0.01
Fe 0.96 Fe 2 0 3 1.90 2.42 2.67
NiO — — —
TOTAL 100.16 CoO - — —
0.05 2.24 2.75
A1 2 0 3
— 0.09 0.15
Mn0 2
CaO 0.05 0.10 0.03
0.76 2.39 2.69
P 2 O 5
0.10 0.05 0.02
S0 3
0.37 3.17 3.20
s i o 2
c o 6.45 1.58 0.05
2
Loss 3 6.32 19.31 21.30
TOTAL 99.83 100.05 100.25
Humus trace trace 0.08
- - —
NH 4
CI 0.05 0.08 0.03

After Geilmann (1956).
Loss of weight on ignition.
l