Page 13 - Copper and Bronze in Art: Corrosion, Colorants, Getty Museum Conservation, By David Scott

P R E F A C E

Actually the use of copper was discovered before that of iron, because it is more easily handled and
in more plentiful supply. With copper they tilled the soil. With copper they whipped up the clashing
waves of war, scattered a withering seed of wounds and made a spoil of flocks andfields Then
by slow degrees the iron sword came to the fore; the bronze sickle fell into disrepute; the ploughman
began to cleave the earth with iron, and on the darklingfield of battle the odds were made even.
— LUCRETIUS 1

Copper has played a crucial role in human development. Just as the compounds of copper found
in nature made possible the extraction of the metal, so corrosion may slowly return these same
copper objects to the minerals from whence they came. This book had its origins as a review of
the literature on this fascinating metal, focused specifically on the corrosion of copper and cop­
per corrosion products or minerals used as colorants. From there, it gradually expanded into a
more ambitious and personal account of the subject, which now includes a review of the envi­
ronmental conditions to which copper alloys may be exposed and the methods used to conserve
them, together with some information on ancient and historical technologies and on the nature
of patina as it pertains to copper and bronze. This book is not intended as a reference text in the
sense of a Smithells (i983) or the CRC Handbook of Chemistry and Physics (Weast 1984), nor does
it cover the smelting, extraction, mining, or alloying of copper, a huge body of information that
would rightly form the subject of a book in itself.
Pigments, corrosion products, and minerals are usually considered separately, either as
painting materials or as the deterioration products of metals, even though they are often the
same compounds. One of the aims of this book is to integrate the information relating to these
materials across a broad spectrum of interests that are all too frequently compartmentalized.
Corrosion can be thought of as an integral part of conservation practice, since the purpose
of conservation is to arrest continued corrosion and the processes of change. Conservation treat­
ments are therefore reviewed here from a chemical perspective rather than from a consideration
of the individual artifact, which might have quite different ramifications. Treatments are also
considered here somewhat in isolation as a means of reviewing the kinds of approaches taken
rather than the variety of artifacts conserved.
Since the subject matter of this book is rooted in copper, alloying elements are dealt with
more briefly. Indeed, the word bronze is used here in a catholic sense —as an ersatz alloy—to
encompass all of the copper alloys commonly employed in the ancient world, much as the term
Renaissance bronzes covers a diversity of alloys that are, in fact, often brass ternary or even qua­
ternary mixtures of copper, lead, tin, and zinc. When writing about bronze, it is difficult, there­
fore, to fix boundaries to the multifarious alloys that may be found and to the vicissitudes of
their corrosion. The deterioration products of the subsidiary elemental components are men­
tioned here, but they are not comprehensively described.