Marqueta Fragment

This object is most likely a fragment of a marqueta, a wedge-shaped lump of an alloy of silver (92.2%) and mercury (7.2%)—produced during the Patio process, a technique used to extract silver from ore by means of mercury. This truncated object, originally classified as a mace or hatchet fragment, is now recognized as a fragment of pressed silver amalgam that was not fully distilled, and thus retains some of the mercury. In addition to silver and mercury, this marqueta has traces of antimony (0.3%), arsenic (0.4%), and lead (<0.1%).

Developed in Mexico in 1554, the Patio process involved the crushing the silver ore in shallow circular pits known as arrastras. Once reduced to a fine sludge, the ore was spread out in a patio—a low-walled, circular enclosure open to the sky—and mixed with salt, water, copper sulfate, and mercury. Over weeks of mixing, the silver formed an amalgam with the mercury. The final step of the Patio process was to remove the mercury. According to a nineteenth-century treatise, in order for mercury to be fully expelled, the filtered and pressed amalgam was beaten into circular molds, cut in wedge-shaped segments about 2–2 ½ inches thick, and arranged into a cylindrical pile (piña) into a capellina, a bell-shaped furnace designed for the specific purpose of evaporating and condensating the mercury. These segments of metal were called marquetas or ballos, and weighed up to 30 lbs. each (Percy 1880:626–629). The present object appears to be a fragment (1/3) of a marqueta weighing about 10 lbs.

Federico Carò, Associate Research Scientist, 2017

Further reading
Percy, John. 1880. Metallurgy: The Art of Extracting Metals from their Ores. Silver and Gold. Part 1. London: John Murray.