Gilded bronze sculpture in the Athenian Agora

Alice Boccia Paterakis


Several copper alloy statuary  fragments cast by the lost wax method, which preserve traces of gold and silver cladding, have been discovered in the Ancient Agora Excavations. These objects will be reviewed according to condition upon excavation, conservation treatments, technique of manufacture and analysis of core and cladding materials.

In 1932 a Nike head, approximately 1/3 lifesize, was excavated from a well and dates to the 5th c. B.C.1 Grooves which appear to have been chiseled into the surface after casting preserve traces of the gold and silver cladding which they were originally intended to secure. Two periods of channeling have been determined historically. The first cladding may have been removed in 406/405 B.C. to contribute to the dwindling treasury stores of Athens. The head may have been recladded around 336 B.C. when new channels were chiseled into the surface. The channels were carved with a straight-faced chisel to an average depth of 2 mm and width of 1.5 mm or 2.5 mm. The final stripping of the statue was executed with an 8 mm wide straight-faced chisel. The lower edge of the neck has been finished so that it could be fitted mechanically onto the dress or body of the statue. It was stripped of its gold and silver and cast into a well during the first half of the 3rd c. B.C.

This object was covered with copper corrosion products as witnessed by photographs taken shortly after its discovery. The corrosion was removed by electrochemical cleaning with zinc and sodium hydroxide. There are no records of any further treatment since the 1930’s.

In 1971 several fragments of a copper alloy equestrian statue were discovered in a well: a leg, two drapery fragments, a sword, a pegasus from the helmet, several fragments representing leather straps, and fragments of an akroterion palmette.2 This heroic size statue, which has been attributed to represent Demetrios Poliorketes, an officer in Alexander the Great’s army, has been dated to the end of the 4th c. B.C. (Hellenistic period) . Complete the figure would have stood at least 6 feet tall. Most of these fragments resemble the Nike head in that channels were chiseled into the surface after casting in which to secure the gold and silver cladding. The average width of the channels is 2 mm. Evidence for the mechanical attachment of the fragments is found in the projecting flange on the top of the thigh and rivets on the sword for attaching the sword to the torso and the straps to the sword. The maximum thickness of the silver/gold cladding is 0.5 mm. The statue was stripped of its gold and flung down a well around 200 B.C.

Although there are no records of the initial conservation treatment, most of the fragments appear to have been cleaned mechanically with the exception of a few of the akroterion fragments which may have been cleaned electrochemically. The sword was excavated in two pieces which were joined with a copper alloy dowel and gap-filled with an unidentified polyester resin putty. Extensive scratching of the copper alloy surfaces may have occurred during on overly-rigorous mechanical cleaning during the initial treatment phase. In a subsequent conservation intervention in the 1970’s for which written records exist silver corrosion products were removed from some areas of gold with ammonium thiosulphate and areas of active bronze disease were treated with silver oxide and benzotriazole. The silver oxide treatments failed to stabilize the areas of active corrosion whereas the benzotriazole succeeded to stabilize the active areas on all pieces with the exception of the sword. The fragments were lacquered with a cellulose nitrate varnish.

In a more recent conservation intervention recurring bronze disease on the sword was stabilized by total immersion of the object in benzotriazole until corrosive activity ceased. This prolonged immersion necessitated the removal of the polyester putty fill in order to expose all active areas of corrosion. The failure of the former treatment with BTA may be attributed to the fact that it was applied only to those areas which were accessible on the surface. A polyester putty, “Chemical Metal”, was used to fill the central gap. The sword was lacquered with Incralac.

A mixture of calcium carbonate (initially calcium oxide) and bleached beeswax was identified on the interior of the Nike head by chemical analysis and infrared spectroscopy in 1960 by Farnsworth and Simmons.3 This mixture may have served any number of purposes: to cement the eyes in the sockets, to secure the attachment of the copper alloy topknot (not preserved) onto the head or the head onto the body, the secure the gold cladding onto the surface of the statue or the gold in the channels.

The technique used for the cladding of these statues may be generally characterized as the foil gilding technique until results of further analysis are available. A literature review reveals the earliest evidence of the foil gilding technique with the Egyptians in the 3rd millennium B.C. The technique of burnishing gold leaf onto silver followed by interdiffusion upon heating carries on from at least 1200 B.C. into the Hellenistic period. Examination of the Agora fragments revealed the insertion of a metal rod into the channels, presumably to secure the cladding sheets to the surface of the statue.

The copper alloy of most of the fragments was analyzed by Atomic Absorption Spectroscopy at the British Museum in the 1970’s.4 All the equestrian pieces were found to be a heavily leaded tin bronze with the exception of the sword which is a tin bronze. The Nike head is also a tin bronze. The gold and silver cladding from one of the drapery fragments was examined with the Scanning Electron Microscope in the 1970’s by Sheridan and found to be a pure gold layer on top of a pure silver layer.5 Sheridan also determined that the metal rod used to hold the cladding in place in the channels was silver. The exact procedure used for the insertion of these silver rods and the method for attaching the rod to the cladding material has not been clarified.

The purpose of further analysis with the Scanning Electron Microscope and the Electron Microprobe by Scott at the Getty Conservation Institute is to 1) determine the position of the cladding in relation to the metal rod in the channels (the cladding overlies or underlies the metal rod in the channel), 2) identify all materials used in the cladding process (the presence of elements other than silver and gold), 3) determine the form of the gold when it was applied to the silver substrate (foil,leaf,etc.), 4) determine the method of application of the gold to the silver (possible annealing) .6

1T.L. Shear, Hesperia II (1933), pp. 519-527. H.A. Thompson, “A Golden Nike from the Athenian Agora”, Harvard Studies in Classical Archaeology, Suppl. Volume 1, 1940, pp. 183-210.
2T. Leslie Shear Jr., “The Athenian Agora: Excavations of 1971”, Hesperia XLII (1973) pp. 164-173. C. Houser, “Alexander’s Influence on Greek Sculpture As Seen in a Portrait in Athens”, Studies in the History of Art, Vol. 10, National Gallery of Art, Washington, pp. 229-238.
3M. Farnsworth, I. Simmons, “A Unique Cement from Athens”, Hesperia XXIX (1960), pp. 118-122.
4W.A. Oddy, L.B. Vlad, N.D. Meeks, “The Gilding of Bronze Statues in the Greek and Roman World”, The Horses of San Marco, The Royal Academy, Venice 1979, 182-186. Unpublished report from P. Craddock of AAS results of equestrian and Nike statues, 1977.
5Unpublished report from W. Sheridan.
6Analysis to be completed in May 1995.

1995 | St. Paul | Volume 3