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The Patio Process and the Start of Amalgamation Refining

In modern times, we’ve become accustomed to silver being the most inexpensive precious metal. But in the mid-sixteenth century, American silver production went into steep decline as mines that produced high-grade silver ore began to run out. Even though there were many other silver mines, the production and extraction costs were too high to make those mines worthwhile.

Luckily, Bartolomé de Medina – a successful Spanish merchant – took notice of these silver production problems and began working on a solution. While studying and consulting with smelters in his native Spain, Medina learned silver could be extracted from mined ores using mercury and a salt-water brine. With this knowledge, he traveled to Mexico and developed a refining technique that came to be known as the patio process.

During the patio process, silver ore was finely crushed and mixed with salt, water, copper sulfate, and mercury. This mixture was spread in a one to two foot layer in an outdoor patio. After weeks of mixing and sun exposure, the native silver in the ore would bind with the mercury to form an amalgam. After that, pure silver could be extracted more easily than traditional methods.

This large-scale amalgamation process is the first known in the history of precious metal refining. Thanks to Medina and his patio process, the silver mines of the Americas were saved.

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