The beneficio de patio: silver amalgamation in New Spain

The cold amalgamation of silver ore with mercury, salt and roasted copper pyrites, worked in open yards in New Spain from the sixteenth century and still the standard method three hundred years later. It is the process behind the silver that reached China. Two technical witnesses describe it here — a Madrid lawyer of 1761 and a German mineralogist printed in 1825 — and both record its limits: mercury lost, gold left behind, and a chemistry its own practitioners misexplained.