Page 346 - Copper and Bronze in Art: Corrosion, Colorants, Getty Museum Conservation, By David Scott

composition of 35% S η, 7% Cu, 7% Mg, 7% Fe, 2% Μη, 2% Si, and 0.2% Pb; while X-ray diffrac­
tion analysis showed the presence of MgSn(OH) 6 and FeSn (OH) 6—magnesium and iron hexa-
hydroxystannate, respectively. From the published data it is not possible to conclude that the
Riace bronzes actually had a black patina before they were lost at sea. In oxygen-depleted sea­
water, the initial cuprite crust could easily be converted to copper sulfides by natural corrosion
processes under the smoothly deposited sandy concretion. Since the cuprite or original surface
would preserve the original outline of the object, there is no reason why the conversion of the
cuprite to a black sulfide would not result in a smoothly preserved sulfidic patina; fine black
patinas have been noticed on less-impressive objects that were buried at sea.

PATINAS IN T H E R E N A I S S A N C E

The renewed interest in everything antique brought the subject of the patination of bronzes
under close scrutiny during the Renaissance. Weil (i996) searched for the earliest use of the
word "patina" and found a likely candidate in an art dictionary published by Filippo Baldinucci
in 1681. The word is defined there as "the general dark tone that time causes to appear on paint­
ings, that can occasionally be flattering to them" (Weil 1996:398-99)
Yet the use of the term appears to go back even further than the seventeenth-century. For
example, Jaffé (i989) discusses the depiction of a bronze Etruscan mirror fragment in a drawing
by Nicolas Poussin (ca. 1593-I665), titled Studies of Antiquities. 12 Jaffé also notes that a com­
mentary by Peiresc published in Rome in 1590 concerning the distinguished antiquarian Pietrus
Ciacconius (Pedro Chacon, 1527- 8i) included a reference to patina.
Many Renaissance bronzes were finished with a reddish translucent patina that was par­
tially formed by cuprite and overlaid with resinous finishes. The Italian artist Giorgio Vasari
(1511-54) observed that bronzes will naturally darken with time (Vasari [1907] i960). Both he and
the sculptor Pomponius Gauricus (ca. I48i-i528), writing in 1504, prescribed the use of vinegar
to turn the surface green and the use of oil or varnish to produce a black finish (Gaurico 1969).
Green verdigris-like coatings may have been useful for some purposes and may have been a his­
torical reference to earlier, antique bronzes. Such bright green patinas, however, are not particu­
larly attractive on fine Renaissance sculpture and did not really come into vogue in Europe until
the nineteenth century. Vasari writes:

[T]his bronze, which is red when it is worked assumes through time by a natural change
colour that draws towards black. Some turn it black with oil, others with vinegar make it
green, and others with varnish give it the colour of black, so that every one makes it come
as he likes best. (Vasari [1907] i960:165-66)
Some artists, like Leone Leoni (1509-90), used a green varnish to imitate natural patina­
tion, and there is a suspicion that some bronze workers used a thick greenish varnish in an

S O M E A S P E C T S O F B R O N Z E PATINAS
329