The chemical maturity of the process was reached by the end of the sixteenth century, and lasted for three hundred years until a new chemical process based on cyanide displaced it. The refining activity of the patio process hinged around the milling areas and the patio reactor. The arrastre symbolises the high degree of technical innovation reached in New Spain. The patio (courtyard) was an open-air chemical reactor, capable of refining major amounts of silver sulphide ores that did not contain lead, a unique example of a batch industrial process that could extended laterally or contract as needed. The careful recycling of mercury was carried out using desazogaderas or capellina ensembles. The haciendas de patio came in a wide range of sizes, from the small zangarros of Guanajuato to the industrial behemoth at Fresnillo. The imbalance in the spatial requirements of each stage of the patio process is reflected in the architectural footprint of an hacienda de patio, with the patio reactor and milling areas requiring most of the space, while in the final stages of the separation of the amalgam, mercury and silver required smaller areas for the control of possible operational losses or pilfering. The development of this industrial process took place in the New World, with no known input from Europe.