Page 39 - Copper and Bronze in Art: Corrosion, Colorants, Getty Museum Conservation, By David Scott

The deposition of other metals, especially on scientific brass instruments, was often used
during the eighteenth and nineteenth centuries. Bronzing solutions based on arsenic oxide
deposit a thin adherent film of arsenic, as recorded by Fishlock (i976). 6 Patination solutions
based on mercury salts were the most common but also created problems with corrosion of the
copper alloy substrate. Bright red mercuric oxide can often be observed under blisters on dete­
riorated surfaces coated with mercury for which Hiorns (i892) provides a practical recipe. 7
I ELECTROTYPiNG The electrolytic deposition of copper for the
production of electrotypes and the electrolytic dissolution of copper corrosion products for the
cleaning of copper objects represent two different applications of the same electrochemi­
cal principles. In the first case, cathodic deposition of copper is used to build up a replica of
an object; in the second, the cathodic dissolution of corrosion products, using stainless steel
anodes, is used to reveal the remaining metallic surface or core of an object under treatment.
During the period when electrotyping was at its zenith in the nineteenth and early
twentieth centuries, many copper objects were produced from the deposition of copper from
solution, using electric current with copper (II) solutions and copper anodes to replenish the
solution. Opinions vary as to when the first galvanic decomposition of a metal salt solution was
achieved, but the discovery of the voltaic pile by Volta in 1796 made possible the application
of current to salt solutions. The first application of galvanic deposition did not occur, how­
ever, until about 1839, followed by the development of its practical application during the i840s
(Beale 1975).
A colorful array of characters were involved in the early developments of electrotyping.
One of these was Duke Maximilian Hertzog von Leuchtenberg (1817-52), son-in-law of Czar
Nicholas I of Russia, who founded the St. Petersburg Electroforming, Casting, and Mechani­
cal Plant, a firm that produced copper electroforms, as well as copper horses for the Bolshoi
Theatre and copper statues for the Hermitage (Hunt 1973). The Encyclopaedia Britannica (i898)
states that one of the most important activities in electrotyping in England at that time was to

F I G U R E 1. 2 B O X Μ Ϊ Γ Γ Ο Γ
with Modern Relief Pro-
tome. Mirror: Greek,
fourth century B . C . E .
1
Relief Protome: 930.
D I A M : (mirror) 15. 5 cm;
(case) 15.3 cm. Bronze. The
profile of a head on the
back of this mirror appears
perfectly acceptable, but it
is an electrotyped addition.
Malibu, J. Paul Getty
Museum ( 8 5 . A C . 8 7 ) .

C H A P T E R O N E
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