Page 162 - Copper and Bronze in Art: Corrosion, Colorants, Getty Museum Conservation, By David Scott

Basic Sulfates

CHAPTER ζ

What do you think, saidDiogenianos, could be the cause of the colour
of the bronze here? And Theon said, when of the things that are consid­
ered and really are the first and most natural, fire, earth and air and
water, none other comes close to the bronze nor is in contact except only
the air, it is evident that it is affected by this and that. — LUTARCH 1
P

He copper sulfates are important primarily as corrosion prod­
ucts of copper alloys exposed to polluted atmospheres in urban environments. General back­
I
ground information related to the outdoor exposure of copper alloys is reviewed in CHAPTER .
The present discussion provides a more detailed account of how basic sulfates and related com­
pounds form, using data from studies of particular bronzes and from laboratory experiments.
In recent years, valid concerns have been raised that increasingly acidified rain and fog are
dissolving formerly stable patinas that had been slowly developing over time. The severe streak­
ing with light green corrosion running down the surfaces of many neglected bronzes suggests
that some outdoor statuary is indeed being attacked at an accelerated rate under conditions
of very low pH.
In Europe and in North America, atmospheric concentrations of sulfur dioxide are
beginning to fall in many places, but they are often replaced with higher concentrations of the