Page 413 - Copper and Bronze in Art: Corrosion, Colorants, Getty Museum Conservation, By David Scott

Notes
1 Calgon is often stated to be sodium hexameta- 8 In this treatment, an outer wax coating is applied
phosphate, but according to King (i996) , it is not that can be regarded as a sacrificial layer, in that it
really a hexametaphosphate but rather a poly­ may be damaged by wear and can be reapplied at
phosphate of composition (NaP0 3 ) 15 _ 20 . regular intervals before the underlying coatings
2 Because of the widespread use of electrochemi­ are also damaged and require replacement.
cal and electrolytic techniques from 1910 to 1930, 9 Walnut shells of 6O/20 0 mesh were used at a pres­
4
many of the stripped bronzes were subsequently sure of 0 psig.
repatinated as part of the conservation treatment. 10 Graphite anodes were used as an alternative, but
Plenderleith and Werner (1971) mention a simple any carbon that became attached to the object dur­
method that was widely used for many years: the ing treatment was very difficult to remove, and
freshly cleaned bronze surface would be coated often it could not be removed safely.
with warm Plasticine, a nondrying oil-based clay 11 This bronze was re-treated quite a few times
containing considerable amounts of sulfur, that employing mechanical cleaning methods, as dis­
was left on overnight. In the morning, the Plas­ cussed earlier; for localized bronze disease corro­
ticine would be removed with methylated spirit sion, some spots were also treated with the silver
(denatured ethanol usually containing additions oxide paste in ethanol and water.
of pyridine, methanol, and a blue or pink dye), 12 Susan L. Maish, conversation with the author,
revealing a rich brown-black patina of copper March 1996.
sulfide. Such patinas also formed accidentally in 13 Ammonia is commonly available as a solution in
old storage cabinets where Plasticine had been water. The concentration of ammonium hydrox­
used previously as a mount or temporary gap- ide solutions is conveniently measured by its spe­
(
filling material. J. Twilley noted in a conversation cific gravity SG), 0.88 being the most concentrated
with the author in 1998 that the whiskerlike crys­ solution usually employed.
tal growth on metallographic sections stored on 14 Josef Ternbach is one of the pioneers of mechani­
Plasticine-mounted glass slides was primarily cal cleaning at a time when most workers sim­
chalcanthite. ply reached for the bottle of chemical reagent.
3 In 1910 Henry Walters was in charge of the Wal­ Many bronzes were mechanically cleaned by
ters Collection, later the Walters Art Gallery. On him between 1950 and 1970.
Walters's death in 1931, the gallery was bequeathed 15 H. B. Madsen, conversation with the author,
to the mayor and city council of Baltimore. Copenhagen, September 1981.
4 Formerly the National Museum of the American 16 Electrolytic desalination is a process in which
Indian, Heye Foundation, located in New York; the bronze object is wired to a source of cur­
now the National Museum of the American Indian rent and used as the cathode, with platinum-
in Washington, D.C., held in trust by the Smith­ or molybdenum-stabilized stainless steel anodes.
sonian Institution for the State of New York. A low current is then generated and chlorides
5 A bronze vessel from the site of Hallstatt in the removed from the object.
Austrian Salzkammergut, 0 miles east of Salz­ 17 Hykin has pointed out, however, that octylphe-
3
burg, famous for its salt mines and cemetery of nols are not biodegradable and are estrogen mim-
three thousand graves dating to the twelfth cen­ ickers that have been shown to cause damage to
tury B . C . E . fish and amphibians. Therefore, their use as a
6 The Vix krater is from a famous Celtic burial site cleaning solution may not, in fact, be advisable at
of the Early Iron Age located at Châtillon-sur- all, unless disposal options are carefull evaluated
Seine, Côte-d'Or, France. The krater is of Greek (Abby Hykin, letter to the author, 16 April 1998).
manufacture and stands 152.4 cm (5 ft.) high with 18 The core material is that part of the investment
a capacity of 1250 1. filled with a refractory substance that produces
7 Glass-bead peening— or air-abrasive cleaning the hollow region in castings. The core, often of
using glass beads, as it is otherwise known— clay and charcoal, clay and sand, and sometimes
employs a compressor supplying a jet of air with added organic temper such as straw, rice-
through which small particles, such as glass beads, husks, dung, etc., is generally removed after the
crushed walnut shells, or alumina powder can be object is cast, since it may absorb salts and create
forced against the surface to be treated using an problems with the long-term stability of the object.
air pen, usually operated in a hood with gloves 19 As has been discussed, these citric acid solutions
and glass screen between the operator and the are capable of changing the patina, so their use
object being treated. would need to be evaluated accordingly.

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