The Ancient Secret of Pre-Hispanic Jewellery

Introduction

The ‘lost-wax’ technique of jewellery casting began in the northern half of South America, in Colombia, Peru and also Costa Rica, and reached Mesoamerica between 800 and 600 BCE. ‘Lost-wax’ casting is the most complex of all jewellery-making techniques as it involves a series of crucial stages, mistakes during any of which can affect the quality of the end product. Pieces of jewellery made with this technique are larger in volume, design and texture than those obtained using any other method.
In pre-Hispanic societies, any metal used in jewellery had a mystical significance, tied to its transformation, continuity and regeneration, rooted in ancient views of the origin of the universe. Each design would be associated with magical powers that would be transferred to its bearer during rituals and ceremonies. In Mesoamerica small bells were the most widely produced pieces of jewellery, and incorporated a rich variety of shapes, depicting animals, plants, gods and mythical beings.

Pic 1: Mixtec gold pendant depicting a ruler with ritual regalia, British Museum

It’s more than likely, therefore, that in the mind of the pre-Hispanic goldsmith, creativity and technical procedures went hand-in-hand during the fashioning of a jewel: he had to juggle simultaneously cultural and religious elements alongside the important physical details that would allow the piece to be cast in metal (its thickness and size, melting temperatures for both metal and mold, etc.).
Today, our most important source of information for pre-Hispanic jewellery manufacture is the descriptions contained in the Florentine Codex, compiled between 1548 and 1561 and provided by local craftsworkers for Fray Bernardino de Sahagún. Seeing in this document the simplicity of materials needed to produce a jewel (clay, charcoal, beeswax, copal incense, tubes...) one can’t help but wonder if Aztec goldsmiths didn’t possess some ‘secret to ancient casting’ in order to create such fine and delicate pieces of jewellery – which today can only be matched with the aid of modern technology. Indeed, what method today could be considered the ‘Holy Grail’ of pre-Hispanic goldsmithery?

The literature on pre-Columbian metallurgy contains few studies by writers who have experimented with ancient techniques of casting jewellery using the lost-wax method, and unfortunately a few of these have introduced modern equipment and/or materials into their research, making it hard to draw firm conclusions from their results as to exactly how things were done in ancient times.

Pic 3: Chapter 16, Book IX of the Florentine Codex, which gives a detailed description of the processes involved in Aztec precious metalwork

The experimental stages followed in making the test designs, based on the ancient lost-wax formula of creating a wax model that is subsequently turned into metal through the process known as ‘casting’, were these:-
a) Mixing of beeswax with copal incense
b) Forming the core in clay and charcoal
c) Creating the design in wax
d) Making the clay mold
e) Inserting the casting channel
f) Forming the casting funnel
g) Removing the wax and firing the cast
h) Casting and pouring of the metal.

Pic 5: Raúl Ybarra experimenting with Jesús García Zavala, Michoacán

b) Forming the core in clay and charcoal. In order for the figures to be hollow and not solid after casting, a clay and charcoal core has to be created, the same size and shape as the final object. The cores used in our work comprised 40% coal dust and 60% clay.
c) Creating the design in wax. After preparing the beeswax and copal incense mix, the designs were created based on archaeological examples from different pre-Hispanic regions of Mexico. In such cases the wax thread was wound round the clay and charcoal core.

Pic 7: Application of charcoal and water paste, Florentine Codex Book IX

f) Forming the casting funnel. The mold’s funnel was then made of charcoal and clay and placed around each design’s casting channel, to direct the metal inside (Pic 9).
g) Removing the wax and firing the cast. Once dried, the molds were placed in an oven for two hours, for the wax inside to melt and for the clay to be fired.
h) Casting and pouring of the metal. The metal used to form the designs was pure copper and bronze (copper with 5% tin). The metal was melted in a spoon-shaped crucible made of the same materials as the molds. The crucible and metal were placed in a clay brazier, into which air from the lungs was blown through several reed tubes with a nozzle at one end, allowing the air to be introduced in amongst the coals, and so raising the temperature of the brazier. Once the metal had melted, it was poured inside the mold, which could subsequently be opened to determine the quality of the jewellery piece.

Pic 9: Experimental clay molds made by Raúl Ybarra

The absence of ventilation channels (or signs of these) was one of the most important characteristics found in the designs on display in different museums. This helped us gauge the experimental ratios of charcoal and clay to use in the molds in order to achieve the right level of porosity (empty space) which would lead to complete designs in finished metal.
The absence of a bracket or support for the clay core was found not to affect its internal strength, and complete designs could be achieved since the semi-watery covering of charcoal and clay, on coming into contact with the exposed part of the core, formed a temporary support after the drying stage. This underlines, albeit indirectly, the importance of using this type of mixture in the original process; it also encourages the detailed reproduction of textures in the metal design.

Pic 11: Experimental charms in bronze and copper (top) and experimental copper bells (bottom) by Raúl Ybarra

Studies of the structure and form of pre-Hispanic jewellery and bells, alongside detailed analysis of the Florentine Codex, proved crucial for understanding more of just how these designs could have been made, and for succeeding in reconstructing some similar pieces.
Our results confirm that it is possible to cast jewellery successfully using the lost wax technique, without the need for modern equipment, material or technologies, and that the Florentine Codex contains all the technical details needed.
Finally, it’s clear that further studies are needed to fully explain the manufacturing processes involved in the different styles of jewellery (earrings, charms, pendants, rings, etc.) made by our pre-Hispanic gold and silversmiths. At the present time we still cannot claim that the secret of ‘ancient casting’ has finally been revealed.

Pic 13: Gold ornament with bells, Florentine Codex Book IX