The first recorded history of leaching silver ores with a chloride leach solution is in the Pyrotechnia by Beringuccio, published in Italy in 1540. No doubt it had been practiced for many centuries before that.

It was brought to Pachuca, Mexico by Bartolome de Medina in 1554 as the Patio Process. In the patio process, ore was mixed on a large stone work floor (a patio) with common salt and ferric iron salts, and reacted for several days. This oxidized the sulfide minerals and liberated silver as native silver or reprecipitated metallic silver from silver sulfides. It was then mixed with mercury which amalgamated with the silver. The mercury was then separated from the ore and evaporated to recover silver.

The Patio Process was brought to Potosi, Bolivia, in 1590 as the Buytron Process. The only difference between the two is that the Buytron Process was done on hot patios - stone floors built above long flues from fireboxes. This was required because of the very cold temperatures at Potosi. The process we now use at Itos is essentially the same process - we leach silver using a hot solution of common salt and ferric salts.