Page 374 - Copper and Bronze in Art: Corrosion, Colorants, Getty Museum Conservation, By David Scott

Preservation Some curators never allowed the bronzes in their care to be con-
without treatment served. This is often the case with many collections of Chinese
art, where the aesthetically pleasing patinas of Chinese bronzes
are highly prized and preserved without treatment. This is exemplified by the fang lei men­
tioned in CHAPTER 3 (see PLATE 19). This wine vessel, dating to the fifth to the fourth century
B.C.E. of the Eastern Zhou dynasty, is elaborately and skillfully inlaid with malachite that is
set in intaglio within the borders of the copper strips with a white cement. Subtle banding in
the malachite inlays is still visible. The copper strips have corroded to a light green, while the
bronze vessel itself is generally a darker green, both colors contrasting subtly with the green of
the malachite. Originally, the copper strips would have been reddish, complementing the golden
surface of the bronze and the green of the malachite.
This fang lei presents a surface patina of extraordinary interest. One of the problems with
treating such surfaces is the danger of altering their aesthetics. Benzotriazole, for example, may
darken some patinas through interactions with copper minerals, such as chlorides. The use of
this corrosion inhibitor may be inadvisable on surfaces as complex as the fang lei discussed here.

M E C H A N I C A L C L E A N I N G
Preserving evidence Although thermodynamically less damaging than chemical
of the past cleaning, mechanical cleaning may remove evidence of materi­
als, such as burial conditions and corrosion chemistry, adhering
to the surface of an object. This evidence is lost forever when these products are removed. In a
paper dealing with the mechanical cleaning of some Egyptian bronzes, Jedrzejewska (1976)
made a clear case for leaving some bronzes uncleaned to serve as archaeological records in their
own right. For those bronzes that are cleaned, she advocated that a small area of the surface be
i
left untreated, f at all possible, to serve as a record of the true state of the original patina. Over
the last twenty years this wise advice all too often has not been heeded by conservators; conse­
quently, a considerable amount of information has been lost because of conservation carried out
without regard to the scientific principles of preservation of evidence.
There is a clear need to support and encourage the principle of evidence preservation, espe­
cially among conservators working in private practice who may not have the time or resources
to conduct proper documentation. Awareness has gradually spread through the profession, and
there is now much less invasive mechanical cleaning; the point still needs to be stressed, how­
ever, that many bronzes are visually attractive and stable when left covered in their origi­
nal aeruginous coat. Such an object can also testify to its own burial and authenticity, which
a cleaned bronze may no longer have the power to do. The British art critic and author John
Ruskin (1819-1900) would surely have appreciated this approach of benign neglect, although it
might not always be justified by the particular needs or circumstances of an object.

C O N S E R V A T I O N T R E A T M E N T S F O R B R O N Z E O B J E C T S
357