Page 339 - Copper and Bronze in Art: Corrosion, Colorants, Getty Museum Conservation, By David Scott

Some Aspects of Bronze Patinas

CHAPTER W

Ρ

I atinas have been an object of fascination for thousands of years
and have given rise to most of the compounds discussed in this book. In this chapter, various
aspects of patina are considered in the context of bronze corrosion and with reference to some
of the compounds discussed in earlier chapters.
As Smith rather cryptically remarks, corrosion can be broadly considered as "the move­
ment of interphase interfaces," and its chemistry is that of heterogeneous systems in general
(Smith 1977:143). By "interphase interfaces," he is referring to the phase boundary region
between events. Events that occur during corrosion can be thought of as a boundary system in
which the solid metal substrate is attacked by or interacts with liquid or gaseous substances that
impinge on it. The movement of the interface is, therefore, the corrosion event itself, and inter­
phase interfaces are what make up the corrosion crust — or patina — of copper alloys.
One of the principal problems inherent in any discussion of patina with respect to bronzes
is understanding the nature of the changes to the object's surface over time, whether during bur-