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Liquation is a metallurgical process used for separating precious metals from ores by heating them until the metal with a lower melting point is discharged. It was first used in the 16th century in Germany to separate silver from copper using lead as a solvent. The process is time-consuming and can give ambiguous results, but it was important during the Renaissance period for its massive production of silver, which is believed to have revived much of the European economy.
Liquation is a commonly used metallurgical process that began about 600 years ago. It is a way of separating precious metals from ores that are a mixture of two or more precious metals, by a process of heating the ore until the metal with a lower melting point is discharged. The purification of metals dates back to ancient times, with methods for purifying gold dating back to 6,000 BC The liquation process does not go back that far, as it only works well with certain types of natural alloys and is a specialized process.
Until the 13th century, only seven metals were known to exist in nature: gold, silver, copper, mercury, tin, iron and lead. Until the early 17th century, metallurgical practice for separating metals from ore most commonly involved introducing carbon or hydrogen compounds into the furnace. Germany began widespread use of the liquation practice in the 16th century to separate silver from copper, when Georg Agricola described the liquation process in his 13th book, On the Nature of Metals.
The first two uses for liquation were to separate silver from copper with lead as a solvent and to remove tin from different types of ores. For the liquation to work, it must be done in the absence of air when lead is used, as lead would not serve as a suitable solvent and would separate into litharge, otherwise, a solid earthy and poisonous form of lead with the chemical formula PbO. For this reason the liquation cannot be performed in a normal melting furnace.
Metallurgical processes for liquation initially result in only partial separation of the metals from the alloys. A typical copper-silver alloy can produce liquefied lead which still contains 1-3% copper, 10-30% lead, and the remainder as silver. The process is continued until there is sufficient silver in the liquated lead which is drained off and this mixture is then cupped or further refined in the bottom of the furnace. A further metallurgical method known as desiccation is then performed, essentially an extension of the liquation process to remove more lead from the remaining silver.
Although it seems simple and straightforward, the liquation process is time-consuming, requires special furnace conditions, and can give ambiguous results regarding the final composition percentages of the metal. Metal is also lost in the process as slag and because of this and the length of the process, liquation has now been replaced by more efficient metallurgical methods. However, liquation was so useful during the Renaissance period of history for its massive production of silver that it is said to rival the invention of printing in importance, and is believed to have revived much of the European economy of the 15th and XVI century. centuries.
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