Page 372 - Copper and Bronze in Art: Corrosion, Colorants, Getty Museum Conservation, By David Scott

Although sodium sesquicarbonate treatment was often used in the past, more drastic chem­
ical methods were also commonplace. For example, a bronze might first be immersed in a solu­
tion of Calgon (sodium polyphosphate), then boiled in alkaline Rochelle salt (sodium potassium
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tartrate and sodium hydroxide), then boiled in dilute sulfuric acid, and finally returned to the
Calgon solution. Immersion in Calgon and boiling in 10% sulfuric acid were often used as pre-
treatments before electrolytic reduction. Jaeschke andjaeschke found several variations of dif­
ferent chemical applications recorded in the treatment files at the Petrie Museum.
Dramatic examples of the damage done by overzealous chemical or electrolytic cleaning
are found in the storerooms of the British Museum located in Islington, London. Housed there
are ancient Peruvian mace heads of arsenical copper or tin bronze that are now so honeycombed
that they bear more resemblance to brown sponges than to ancient bronzes. Treatment in the
1930s left a lustrous metallic sheen of freshly stripped metal that has slowly tarnished dur­
ing their sixty years of storage to a sad, tawny brown. These objects are now devoid of any
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aesthetic value, f not of prurient scientific interest for the historical chronicle they represent.
Fortunately, many bronzes that were collected by museums before and during the 1950s and
1960s were never "conserved" at all and have survived in relatively good condition. Some muse­
ums had no conservation staff to carry out treatment until relatively recently. Ironically, some
bronzes in these collections may have survived unscathed, though neglect may have reduced
other more fragile pieces to a heap of unrecognizable fragments.
Early practitioners of conservation were concerned about the adverse consequences of
such drastic treatments and sought to minimize them. Gettens (1933), for example, began tak­
ing X-ray radiographs of bronze objects before attempting electrolytic reduction to ensure that
a sound metallic core remained; otherwise unsuitable artifacts might be converted to green
sludge by the treatment. Beale (i996) notes that by 1956, when Plenderleith was writing his now
classic textbook, The Conservation of Antiquities and Works of Art: Treatment, Repair, and Resto­
ration, advice about reductive methods had progressed to a warning about employing them only
when a substantial metallic core remained and when the mechanical strength of the object was
beyond doubt. 2

Drying and sealing methods Another early and insightful example of how the conservation
of bronzes was regarded at the turn of the twentieth century,
this time from the perspective of a museum director, is contained in correspondence from
Edward Robinson, former director of the Metropolitan Museum of Art in New York. In 1910
Robinson received a letter from the noted collector Henry Walters, asking for advice about
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the conservation of some bronzes. Robinson's response, in correspondence documented by
Drayman-Weisser (1994), was surprisingly sound. He advised keeping the bronzes dry in sealed
cases containing a desiccating agent, such as hydrate of potassia (potassium hydroxide). He also

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