Working with Metals

Goldsmiths as well as miners transformed the materials provided by nature to create these timeless works of art, worthy of admiration. These people were considered wise and sometimes even shamans among their ancient communities. Metallurgy is one of the great achievements of humanity. Since its inception in the Middle East some 9,000 years ago, metalworking has transformed societies and the lives of communities. When humans discovered the malleability, hardness, and resistance of copper, iron, and their alloys, they were able to make tools, weapons, and utensils. Marveled by the beauty of the color and brilliance of gold and silver as well as by the immutability of the former, they also used them to create symbols that legitimized rulers and recreated gods. Metallurgy was invented at different times in different places on the planet. Independent and diverse metallurgical developments emerged in Anatolia, China, the Great Lakes of North America, and in the Central Andes. As was the case in South America, some spread over large territories. The art of gold smithing came to Colombian territories from the south 2,500 years ago. The ancient goldsmiths of this territory continued the tradition of experimenting with gold, copper and their alloys, and invented or perfected various techniques such as lost wax casting or welding by granulation. They even discovered how to work with platinum, a metal that could only be used in Europe since the 18th century due to its high melting temperatures.

Metallurgy and Society

As is the case with technologies in general, metallurgy is intertwined with worldviews, politics, economics, and social organization. When the goldsmith populations of the territories now known as Colombia chose the materials, the manufacturing techniques, and the organization of production, they did so not only under the influence of technical requirements, but also, and mainly, by cultural and social factors. While being a product of society, metallurgy transformed it. Sometime in the early centuries of our era, during the Yotoco Period between 200 BC and 1300 AD, a goldsmith from the Calima region in Valle del Cauca pressed seven thin sheets of gold onto a sea snail. The careful bends and small-staple joints are still noticeable. The natural shell deteriorated, but the gold retained its shape: an extraordinary synthesis of nature and culture.

Territories of Bronze, Gold, and Copper

The first metallurgical evidences of South America have been found in Perú and Ecuador: small hammered sheets of native gold and copper dating back to 1500 BC. Around this time, rulers of Andean societies began to build their power with the use of sumptuous elements such as goldsmith ornaments. Objects manufactured from hammered sheets made of copper and bronze alloys prevailed in southern South America. The first evidences in the Colombian territory are hammered gold works from 500 BC. Complex techniques such as lost wax smelting and gold and copper alloys were developed here, which then passed to Central America and the Caribbean.

Mining and Refinement

Miners were respected and esteemed specialists thanks to their knowledge of the secrets of the earth and the means to extract metals. The goldsmiths also had a double status, combining technical and supernatural knowledge in their work. Many of them served as religious and political leaders. Gold and copper, together with platinum and silver, to a lesser extent, were the metals used in pre-Hispanic times in the Colombian territory. Thanks to bartering, many peoples who did not practice mining were able to acquire the metals needed for their goldsmith work. The mountainous areas of the country are the richest in gold, while platinum is found in alluvial deposits in Chocó, Cauca, and Nariño. Copper was obtained from minerals such as malachite, azurite, or chalcopirite, which are common in the geological layers of the mountain ranges. Native copper is found in the Serranía del Perijá, in Antioquia, and in the south of the country. In nature, gold frequently presents impurities of silver and other metals. It is known as argentiferous gold. Silver contents affect both its color and its physical and chemical properties. No specific mining of silver appears to have existed, although it is likely that this metal could have been exploited in Nariño. The tools of ancient miners were stone axes and hammers and wooden bars with fire-hardened tips. They were used to remove gravel and stones from rivers and to excavate vein mines. As today, the golden sands were washed with ceramic or wood pans by circular movements. The smaller and heavier grains of gold and platinum remained at the bottom. In nature, it is possible to find metals in native state, ready to be worked. However, as in the case of copper, it is more frequent to find them as minerals and oxides that must be melted with fire inside furnaces in reducing atmospheres, that is, without oxygen, to extract the metal. This process is known as the refinement of metals. For this process, furnaces were built high in the mountains where air currents stoked the fire. Portable ceramic burners were also used. Air was blown onto the embers with guadua reeds topped by ceramic tubes to maintain high temperatures. Some blowers with faces show the symbolic importance of transforming the mineral into metal. The metal was then melted in clay crucibles with charcoal and fluxes that helped to extract the impurities. Round ingots or weaves were then ready to be worked upon. Also, metals were mixed in crucibles to obtain alloys such as tumbaga, a combination of argentiferous gold and copper. Goldsmithing Techniques [edit] Goldsmithing is the art of carving objects with precious metals. Goldsmiths materialized their skill and knowledge about the physical and chemical characteristics of metals in the great diversity of manufacturing techniques used by the pre-Hispanic goldsmiths of Colombia.

Hammering and Fire

Metallurgy in the Peruvian Andes was characterized by its emphasis on the production of objects by hammering. This technological preference was a cultural choice that did not depend on the properties of metals or knowledge of other techniques, as goldsmiths knew about foundry, which they carried out before hammering. The Andean tradition spread throughout the Colombian territory, particularly among the societies located in the southwest. To make the sheets, the goldsmiths beat weaves on slabs or stone anvils. They used hammers of different shapes, materials, sizes, and weights according to the alloy, the dimension of the object, or the phase of the work. When hammered, metal becomes brittle and tends to fracture. The goldsmiths had to heat it red-hot and cool it by immersing it in water. This process (known as annealing) was repeated many times, allowing them to continue hitting the sheet until the desired thickness and size were obtained. Stone slabs and polishers were used to smoothen the sheets and obtain uniform surfaces. Stone chisels or hammered-hardened tumbaga were used to outline and trim the final shape of the object. The high malleability of gold makes it possible to manufacture thin and flexible sheets to make objects of varied shapes, sizes, and calibers. Silver was used only in the highlands of Nariño due to the cultural influence of the Central Andes. Nose rings, earrings, containers, and diadems were made from copper and silver alloys. Hammered copper ornaments and utensils were usually heavier and thicker than those made of gold or silver. Ornaments hammered in tumbaga, an alloy of gold and copper, usually have thin walls and very polished surfaces.

Embossing and Fretwork

The artist sketched the decorative designs on the back side of the sheet with engravers. Then, using chisels, embossers, and punches, the artist pressed and highlighted the motif on both surfaces to obtain volumes while resting the object on some soft material or on shapes carved in clay, wood, or bone. The designs with empty spaces or open fretwork were obtained by cutting the sheets with metallic and stone chisels.

Sintering

In America, platinum metallurgy only took place in the Tumaco - La Tolita region, on the Pacific Coast of Colombia and Ecuador. Goldsmiths developed sintering because its high melting point (1.775ºC) did not allow them to melt it. When heating platinum granules mixed with gold, the latter melts and traps platinum; the resulting piece could be worked by hammering. A metallographic microscope shows how platinum grains are trapped by molten gold. Goldsmiths from southwestern Colombia combined parts of gold and sintered platinum to create bi-color ornaments.

From Wax to Metal: Lost Wax Casting

Pre-Hispanic goldsmithing in the territory of present-day Colombia stood out in South America thanks to the predominance of smelting with the lost wax technique. Goldsmiths were masters at creating ornaments and containers that they modeled in wax with their hands and then transformed into metal. The wax was obtained from beehives of non-stinging bees, or angelita bees. In Colombia, various species are found from sea level to 3,400 meters, especially in humid forests. By modeling a shape in beeswax and using a cast to shape the metal, goldsmiths created a great variety of objects: realistic or abstract representations, fine metallic fabrics, or heavy ornaments. The fingerprints found on some metal pendants made Europeans think that the natives were kneading and modeling gold directly. The fingerprints remained on the models used for the lost wax casting process. Gold melts at 1,063°C and copper at 1,083°C. When molten together, they change their properties and their melting point can drop to 850°C. This alloy is called tumbaga or guanín, the latter term given to it by the Taínos of the Greater Antilles.

1. The desired figure was modeled in wax. Rolls of the same material were added to the model, leaving ducts through which the metal would flow once the wax melted.
2. The wax model was coated with layers of clay to form the mold. When dry and hard, the cast was then heated to melt the wax and remove it.
3. The liquid metal was emptied into the cast, thus taking the shape of the model.
4. Once the cast had cooled, it was necessary to break it to obtain the metal piece.
5. After removing the object from the mold, the ducts and the funnel were cut, and the object could then be polished. These traces can still be noticed in some objects.

Unions that create Shapes: Assembly

In some societies, goldsmiths preferred to create volumes from hammered sheets assembled with wires, nails, or bends. They also experimented until they discovered how they could join parts by heating the surfaces or using substances that favored bonding between metals. With the mastery of the artisans, gold adopted the forms of models previously carved in wood, bone, or clay. The embossed sheets were joined or assembled together to produce volumes. The model used to be removed, although it could remain under the metal.

Granulation: A Type of Welding

Delicate necklace beads, nose rings, and rings were crafted by joining tiny gold spheres by the sophisticated granulation process. The nuggets were fixed together with an organic glue mixed with copper oxides. With fire, the glue charred and copper joined the spheres at a temperature lower than its melting point, which prevented their deformation. A refractory ceramic mold found in the Calima region shows how molten gold in its concavities formed the nuggets that were then joined by granulation.

Textures, Brightness, and Colors

Color, brightness, texture, and smell were highly appreciated properties among ancient societies and played a major role in their technologies. To control them, goldsmiths developed various metallurgical techniques and innovations such as the creation of a range of alloys with a wide array of colors, as well as sophisticated finishing processes that brought new tones and contrasts to the surfaces. When heating an object made of tumbaga, the copper present in the alloy oxidizes and a dark spot is formed on the surface. The artist removed the oxidized copper with vegetable acids, leaving a thin, superficial layer that was rich in gold which was later polished to achieve an intense golden color. A clover called chulco, Oxalis pubescens, was used to obtain the oxalic acid with which oxides were removed from the surface of parts oxidized by fire. With use or with the passage of time, the surface gold of these objects has suffered wear revealing the tumbaga on the inside. In objects such as the Nariño discs, contrasting colors were obtained by scraping certain areas of the thin layer of surface gold, revealing the reddish color of the alloy. Attacking the surface of objects with a paste of salts or acids made it porous and matte. Other parts, previously protected with resins, remained bright. Light-reflecting ornaments were carefully polished and burnished by goldsmiths with stone and other material polishers; other objects were left unpolished to catch the light. The goldsmiths of the Eastern Cordillera, for example, did not polish the objects intended for offerings.

Early Repair

Goldsmithing artifacts were highly appreciated among pre-Hispanic societies, both for the meanings and stories they contained and for the material, knowledge, and skills involved in their work. For this assessment, many of these objects were repaired by goldsmiths. Some, deteriorated due to intense use, were recomposed with wires, ribbons, or rivets; other objects with manufacturing flaws were repaired with new metal shells, or, as in the filigree earrings of the Caribbean plains, by darting the fabric with metallic threads.

Metals and the Passage of Time

Time and nature try to recover the materials used by the goldsmith. Most metals and their alloys, except gold, usually undergo major transformations with use and then during their burial. The copper present in pre-Hispanic alloys reacts with moisture and soil salts to produce oxides in a process known as corrosion. At the Museum, the conservation and restoration offices seek to stop this deterioration in order to preserve our heritage. The fabric of the mat that covered a deceased person in the middle valley of the Cauca River was printed on the oxide layer on the back of this pectoral. On the obverse, you can see the traces of a seed necklace.

The room: Working with Metals at the Gold Museum

At the room, the mining, refining, and metal work processes behind each and every metal object found at the Gold Museum are revealed. The unique experience of touring a museum is not reproducible on the Internet. The site "Museum Rooms in Bogotá" and its links to "Pre-Hispanic Societies" offer much more information, but necessarily much less emotion and impact than an in-person tour where you can discover first-hand the original objects of art and life of millennial societies. As an invitation to visit the Museum, we gladly welcome you virtually for this introduction to the permanent exhibition.

See also

• El trabajo de los metales