Lydia's Revolution 2: How the Alchemists of Sardis Parted Gold from Silver?

The Lydian Kingdom's invention of electrum coinage in the 7th century BCE marked a breakthrough in economic history. However, inherent in this early form of money was a flaw that prevented its perfection: variability.

The precious metal ratios within electrum, a natural alloy of gold and silver, were not standardized, meaning two coins of the same weight could have different values. This uncertainty was the greatest obstacle to a trust-based monetary system. The solution to this problem was found in the workshops of Sardis, the capital of Lydia, in what was almost an alchemical operation carried out by masters possessing the most advanced metallurgical knowledge of the era. These artisans succeeded in parting gold from silver, not only achieving a technological breakthrough but also laying the foundation for the bimetallic system that would forever change the future of money.  

Archaeological evidence clearly indicates that Sardis was the center of this revolutionary process. Excavations conducted in Sardis in the 1960s uncovered a series of metallurgical workshops dating to the 6th century BCE along the banks of the Pactolus River. Hundreds of small, shallow clay cups (cupels) and furnace remains found in these workshops were evidence of a high-temperature refining process taking place there. Analyses revealed that this process was a gold purification technique called "cementation" or, more specifically, "salt cementation." This method was one of the most sophisticated chemical engineering achievements of the ancient world.  

The process required considerable skill. First, the electrum alloy was hammered into thin sheets or broken into small granules. This increased the metal's surface area, allowing for a more efficient chemical reaction. Next, these electrum pieces were placed in layers within fire-resistant clay vessels, mixed with crushed pottery or brick dust and, most importantly, abundant salt (sodium chloride). Later writers, such as Theophilus, mention the addition of acidic substances like urine to the mixture to accelerate the reaction.  

These vessels, tightly sealed at their mouths, were heated in furnaces for hours, sometimes even up to 24 hours. The critical point here was to maintain the temperature below the melting point of gold (approximately 1064°C) but high enough for silver to react with salt (approximately 800°C). Under the effect of heat, the salt reacted with the clay and other substances, releasing hydrochloric acid and chlorine gas. These aggressive chemicals reacted with the silver in the alloy, transforming it into silver chloride, a volatile compound. The silver chloride, in gaseous form, separated from the alloy and was absorbed into the porous walls of the vessel or the layers of brick dust.  

When the process was complete and the vessels cooled, what remained was almost pure, bright yellow gold. Small gold droplets found in the workshop remains are tangible evidence of the success of this operation. The Lydian alchemists not only purified gold but also did not waste the silver. They later recovered the silver by melting down the clay and brick dust impregnated with silver chloride. This was an incredibly efficient system, both technologically and economically.

This gold parting technique developed in Sardis was the technological key necessary to take the next great step in the history of money. The Lydians now possessed two separate metals of precisely known purity and thus value—pure gold and pure silver—instead of variable and unreliable electrum. This would enable King Alyattes' successor, his son Croesus (Karun), whose name would become synonymous with wealth, to establish the world's first bimetallic monetary system. The anonymous masters of Sardis, at their furnaces, were purifying not only metals but also the future of trade and economy. Without this technological revolution, the saying "as rich as Croesus" might never have come into being.

Source:
https://en.wikipedia.org/wiki/Gold_parting
https://www.researchgate.net/publication/393505550_Salt_silver_and_gold_early_innovations_in_precious_metal_refining
https://www.hobbydb.com/marketplaces/hobbydb/subjects/mint-of-sardis-mint