Liquation
 | This article's lead section may be too short to adequately summarize the key points. (February 2023) |
Liquation is a
The 16th-century process of separating copper and silver using liquation, described by
History
The first known use of liquation on a large scale was in Germany in the mid-15th century. Metal workers had long known that Central European copper ore was rich in silver, so it was only a matter of time until a method was discovered that could separate the two metals.[3]
Liquation is first documented in the archives of the municipal
This is often regarded as the beginning of liquation, but evidence suggests liquation may have existed in smaller-scale use centuries earlier. The sophisticated nature of the 15th century liquation plants with custom-made furnaces would be surprising for a new technology. There was also a far simpler but more labour-intensive version of the method brought to Japan by the Portuguese in 1591; this is possibly the remnants of an earlier European method.[4]
Agricola discusses various types of copper produced from the liquation process; one of these is caldarium or ‘cauldron copper’ which contains a high level of lead and was used to make medieval cauldrons. Analysis of 13th century cauldrons shows that they are made out of copper with a low level of silver and high levels of lead which would match that produced by liquation.[5]
Liquation may even have existed as early as the 12th century; in Theophilus’ On Divers Arts he makes a possible reference to liquation.[4] However, he was not an expert in metallurgy, so his writings may not be accurate, and though there were similar cauldrons in the 12th century, no compositional analysis has been published that supports this theory.[5]
Against the idea that this process was used significantly before it became widespread in the mid-15th century, is the fact that it had to be done on a large-scale to be financially viable. There is no evidence of large-scale liquation before Nuremberg. Also, efficient liquation requires an extremely skilled practitioner. Anyone with that much skill is unlikely to spend much time on something unprofitable.[3]
Some suggest liquation existed even earlier.
Process
Liquation requires that the silver-rich copper first be
The ratio of lead to copper in these cakes is an important factor for the process to work efficiently. Agricola recommended 3 parts copper to 8–12 parts lead. The copper must be assayed to accurately determine how much silver it contains; for copper rich in silver the top end of this ratio was used to make sure the maximum amount of silver possible would end up within the lead. However, there also needs to be enough copper to allow the cakes to keep their shape once most of the lead has drained away; too much copper and it would trap some of the lead within and the process would be very inefficient.[1]
The size of these cakes remained consistent from when Agricola wrote of them in 1556 to the 19th century when the process became obsolete. They were usually 2+1⁄2 to 3+1⁄2 inches (6.4 to 8.9 cm) thick, about 2 feet (0.61 m) in diameter and weighed from 225 to 375 lb (102 to 170 kg). This consistency is not without reason as the size of the cakes is very important to the smooth running of the liquation process. If the cakes are too small, the product would not be worth the time and costs spent on the process, if they are too large then the copper would begin to melt before the maximum amount of lead has drained away.[1]
The cakes are heated in a liquation
The older and relatively simple method of cupellation can then be used to separate the silver from the lead. If the lead is assayed and found not to contain enough silver to make the cupellation process worthwhile it is reused in liquation cakes until it has sufficient silver.[1]
The ‘exhausted liquation cakes’ which still contain some lead and silver are ‘dried’ in a special furnace which is heated to a higher temperature under oxidising conditions. This is essentially just another stage of liquation and most of the remaining lead is expelled and oxidised to form liquation thorns, though some remains as lead metal. The copper can then be refined to remove other impurities and produce copper metal.[1]
Waste products can be reused to produce new liquation cakes to try to minimise loss of metals, especially silver.[1] The waste products are mostly in the form of liquation thorns from the liquation and the drying process but there are also some slags produced.
Efficiency
This process is not 100% efficient. At the Lautenthal, Altenau, and Sankt Andreasberg smelting-works in the Upper Harz between 1857 and 1860 25% of the silver, 25.1% of the lead and 9.3% of the copper was lost. Some of this is lost in slag that is not worth reusing, some is lost by what is termed ‘burning’, and some of the silver is lost to the refined copper.[8] It is clear therefore that a constant supply of lead was needed to make up for that lost at various stages.
Importance
John U. Nef, an expert on
Liquation triggered an increase in mining operations, and a new class of wealthy
Many new copper and silver mines sprang up. A mine at
Liquation-based wealth helped build roads between mining and processing regions, and financed improvements to mining technology. Thus its influence went beyond just increasing silver and copper production. It helped revive the economy of large parts of Europe, and the mining of other metals such as iron and mercury.
References
- ^ a b c d e f g h Hoover, H.C. and Hoover L.H., 1950. De re metallica / Georgius Agricola. New York: Dover.
- ^ a b c Sisco, A.G. and Smith, C.S., 1951. Lazarus Ercker’s Treatise on ores and assaying. Chicago, Ill.: University of Chicago Press.
- ^ ISBN 1861891733
- ^ a b Hawthorne, J.G. and Smith, C.S., 1976. On Divers Arts by Theophilus. Chicago; London: University of Chicago Press. ‘When the stone begins to soften, lead flows out through certain small cavities and copper is left inside.’
- ^ a b c Dungworth, D. & Nicholas, M., 2004. Caldarium? An antimony bronze used for medieval and post-medieval cast domestic vessels in Historical metallurgy : journal of the Historical Metallurgy Society, 38(1), pp. 24–34.
- ^ Kalyanaraman, S., 1998. Electrum, gold, silver: Soma in the Rigveda. https://www.scribd.com/doc/2670091/Electrum-Gold-and-Silver
- ^ a b Tylecote, R. F., 1992. A history of metallurgy. 2nd ed. London: Institute of Metals.
- ^ Percy, J., 1880. Metallurgy: the art of extracting metals from their ores: Silver and Gold. London: John Murray.
- ^ a b c Nef, J.U., 1941. Industrial Europe at the Time of the Reformation (ca. 1515 – ca. 1540). The Journal of Political Economy, Vol. 49, No. 1 (Feb), pp. 1–40. Chicago: University of Chicago Press.
- ^ Nef, J.U., 1987. Mining and metallurgy in medieval civilization from (ed) Pastan, M.M., The Cambridge economic history of Europe, Vol. 2: Trade and industry in the Middle Ages pp. 691–761. Cambridge: Cambridge University Press.