Fleming, S.J. 1992:
Appendix A: Goldworking Techniques at Sitio Conte: Hammering and Casting, in
River of Gold: Precolumbian Treasures from Sitio Conte.
University of Pennsylvania Museum, Philadelphia.
Just as the gold artifacts recovered from the Precolumbian cemetery at Sitio Conte, in Panama,
displays several different stylistic aspects, so the processes by which they was produced are
also quite varied. Technical studies that were carried out during the preparatory phases of
the Museum's exhibition, River of Gold: Precolumbian Treasures from Sitio
Conte, allowed the three main methods of manufacture-simple hammering of thin foils,
more complex shaping of thicker sheets, and casting of modeled jewelry-to be illustrated in some detail.
For more information of this research, see Appendix A in the exhibition catalogue,
River of Gold: Precolumbian Treasures from Sitio Conte. Appendix B in that catalogue
discusses the technical aspects of the unusual gold/copper alloy (tumbaga), from which all
these artifacts were made, and the technology of depletion gilding, by which the surface
luster of a tumbaga alloy is dramatically enhanced.
A body plaque from Burial 11 at Sitio Conte
To create this plaque, a slab of tumbaga was heated repeatedly and hammered on a stone anvil
until it was wafer thick. What was to be the plaque's front was then taken through the chemical
process of depletion gilding, before being lightly rubbed, to enhance the golden appearance.
Outlines of the design elements were scored onto the plaque's surface; then each was
brought out into relief by pressing all the lines and curves against a yielding material such
as wood or leather. A final burnishing with a bone tool gave the plaque an intense golden sheen.
A human-headed pendant from Burial 11 at Sitio Conte
The first step in making this pendant was to create a wax model of it over a rough core of sun-dried clay.
Several wax tubes and a cone-shaped funnel were added, to serve as vents during the casting process.
The wax model was then covered with wet clay to make the casting-mold, and wooden pins were pushed
right through this mold and the wax model, so that the mold and inner core would stay aligned.
The outer mold was allowed to dry out in the sun; then the whole unit was baked, to melt out
the wax. This produced a hollow, but sturdy clay shell that retained a negative impression of
the pendant on its inner surface.
With the mold kept hot, molten tumbaga was poured into it. Surplus alloy flowed out of the added
vents, so that any pockets of gas that might have left blemishes on the casting's surface were
forced out of the mold cavity. When cool, the pendant was broken out of the mold, and all the
vent rods and residual metal spurs around the funnel were snapped off. Finally, the pendant's
surface was burnished to give it an intense golden sheen.
Frontal x-ray of the human pendant
Courtesy: Radiology Dept., Hospital of the University of Pennsylvania
Remnants of the inner casting core are apparent in the pendant's body cavity and upper limbs.
The thickness of the head's metal obscures the fact that it is full of core material as well.