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Title: Refinement of metals
Original Title: Affinage des métaux
Volume and Page: Vol. 1 (1751), p. 160
Author: Paul-Jacques Malouin (biography)
Translator: Audra Merfeld-Langston [Missouri University of Science and Technology]; Emily A. Weigel [Missouri University of Science and Technology]
Subject terms:
Original Version (ARTFL): Link

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Citation (MLA): Malouin, Paul-Jacques. "Refinement of metals." The Encyclopedia of Diderot & d'Alembert Collaborative Translation Project. Translated by Audra Merfeld-Langston and Emily A. Weigel. Ann Arbor: Michigan Publishing, University of Michigan Library, 2015. Web. [fill in today's date in the form 18 Apr. 2009 and remove square brackets]. <>. Trans. of "Affinage des métaux," Encyclopédie ou Dictionnaire raisonné des sciences, des arts et des métiers, vol. 1. Paris, 1751.
Citation (Chicago): Malouin, Paul-Jacques. "Refinement of metals." The Encyclopedia of Diderot & d'Alembert Collaborative Translation Project. Translated by Audra Merfeld-Langston and Emily A. Weigel. Ann Arbor: Michigan Publishing, University of Michigan Library, 2015. (accessed [fill in today's date in the form April 18, 2009 and remove square brackets]). Originally published as "Affinage des métaux," Encyclopédie ou Dictionnaire raisonné des sciences, des arts et des métiers, 1:160 (Paris, 1751).

Refinement of metals is practiced differently in different countries and according to the different views of those who do the refining . For refining silver, there is a lead method, which is done with a well-dried, red-hot cupel heated in a reverberating furnace. Then, lead is added. The quantity of lead used is not always the same. You use more or less lead depending on whether the silver that you want to refine is suspected of having many or few alloys. To know how much lead is needed, put one part silver with two parts lead in the cupel. And if you see that the button of silver is not very clean, add more lead, little by little, until you have put in enough. Then calculate the amount of lead that you used, so you will know how much is necessary to refine the silver. Let the lead melt before adding the silver, and also the litharge that forms on the molten lead must melt. This is what is called in artistic terms bare lead or lead sheet . If you were to put the silver in too soon, you would risk the material jumping out. If, on the contrary, you delayed longer than it takes for the lead to become bare, you would ruin the procedure because the lead would be overly weakened by calcination.

Once the lead is bare, put in the silver. If you wrap the silver, it is better to do so in lead foil than in paper because it is possible that the paper would remain in the cupel.

The silver melts in the cupel, and revolves nonstop, bottom to top and top to bottom, forming globules that grow more and more as the mass diminishes. Finally, these globules, which some call flowers , lessen in number and become so big that they reduce to one that covers all of the matter while making a flash or sparkle; then it stays still. When the silver is in this state it is called opalescent , and during this time it again appears to revolve. Finally, you no longer see it move; it appears red, then it blanches, and you can hardly distinguish it from the cupel. In this state it no longer moves. If you pull it too quickly while it is still revolving, the air will strike it and cause stagnation, and it will become spiraled or altogether spiked, and it will sometimes come out of the cupel.

There are some differences between small-scale and large-scale cupeling: for example, while refining on a large scale, air must be blown on the cupel while the silver is revolving, to separate it from the litharge. You introduce a runoff flow for the litharge while opening a vent on the edge of the cupel, and you remove the litharge with a rake. If the worker does a poor job, you will find lead and sometimes silver in the litharge. That does not happen when you do small-scale cupeling. In this procedure you should count on sixteen parts of lead for each part impurity.

The refinement of silver by saltpeter is done while melting silver in a crucible in a vented furnace. When the silver has melted it is known as being in bath ; with the silver in this state, you throw saltpeter into the crucible and let everything melt together well. This is called brazing the material in bath .

Remove the crucible from the fire and pour at an angle into a small tub filled with water where the silver becomes ball-like, provided that you are stirring the water with a stick or in some other way. If the water is still, the silver conglomerates.

You also must melt the silver three times while adding saltpeter and a little borax to it each time. And the third time, let the crucible cool without touching it, and pour it into an ingot mold. Then break it open and you will find a fine silver residue. The slag, which is on top, is composed of the saltpeter and impurities that were in the silver.

Use two ounces of saltpeter and a lot of borax calcined by the dregs of the silver. Repeat as long as the slag still has color.

You can refine gold by using potassium nitrate (saltpeter) in the same manner as refining silver, except that you must not use borax because it ruins the color of the gold. Gold mixed with silver cannot be refined by saltpeter.

The refinement of gold is done by melting the gold in a crucible and adding, little by little, when the gold is melted, four times as much antimony. When it is all in a perfectly melted state, pour the matter into the mold and as soon as it cools, separate the slag from the metal. Then melt this metal over an open fire with air blowing to drive off the antimony. Or to finish sooner, throw in saltpeter at different times of the recovery process.

Antimony is better than lead at refining gold only because it carries away the silver, whereas the lead leaves it behind, and it even adds some.

There is the refinement of gold by the quarter sheet method, which is done by using nitric acid, which dissolves the impurity out of the gold and then separates the two. This refinement can only be done when the quantity of impurities greatly surpasses the quantity of gold. The matter must be comprised of one-fourth gold. Refinement can be done if there is more, but it does not work very well if it has less.

You can also refine gold by the cementation method, by putting layer upon layer of sheets of gold and of cement composed of powdered brick, ammonium salt and sodium chloride; then calcining it all over a fire. There are those who also add vitriol, others who use verdigris, etc.

To refine , v. adj. to make purer: to refine silver is to purify this metal from all the metals that could be mixed in with it, completely separating them from the silver.

To refine is also neuter: one can say the gold becomes refined , etc. [1]

A refiner , [masculine] n. one who refines gold, silver, etc.

Refinery , [feminine] n. the place where one purifies metals, sugar, etc. Refinery also refers to refined iron. [2]

There are those who use similar words to those defined above, but they are more commonly used in the moral sense as opposed to the physical sense. See the articles on metals for more on these different refinery definitions. [3]


1. Editor’s note: The French is “l’or s’affine”, which has an adjectival sense by way of “affine” standing in for the past participle, “affiné”. Once taken in adjectival sense “refined” without gender can be paired with its masculine noun.

2. Translators’ note: We have eliminated one sentence here, whose meaning is unclear. It reads, “On peut dire, j’ai acheté tant de milliers d’affinerie ” (“One can say, ‘I bought so many thousands of _____.”) It is not clear what the “tant de milliers” (“so many thousands”) refers to, as it could be refineries or a quantity of refined iron. The former seems unlikely, but there is no specific unit of measurement to explain the latter option either.

3. In place of “There are those who use similar words,” the original French reads, “Il y en a qui dissent raffiner, raffinement, raffineur & raffiné ...”