The Coupellation is a type of test to test the noble metals (goldsmithery or coining; historical context: Republic of Venice). See also Touchau and Peggio

Towards the end of the 13th century diffuses a worked out technique, coming from France, the cupellation or cupels (in Venice: it sazzo , sometimes named " test by the feu" : sazzo per via di foco ). She in fact is known since of the glosses, Theophilus Presbyter (pseudonym of a monk of the Benedictine abbey of Helmarhausen) clearly describing the cupellation of the money since 1110-1140, in a technical treaty written for the monasteries. In truth this method seems to be practiced in China several centuries before our era. It would have been introduced into the Mediterranean basin by the Phéniciens and would be attested in the ancient Greece.

It is this time about a true operation of Métallurgie, intended to isolate by Oxydation various metals from an alloy in fusion. It is based on a common characteristic of the Or and money, that not to oxidize with the high temperatures, whereas the Cuivre present in an alloy oxidizes completely. The operator uses a crucible in Phosphate of lime named cup, made ashes of bone of animals.

It was initially advisable to calcine them until obtaining white residues, reduced in a powder passed to the sieve. This one, placed in a linen, was then put to soak in a bucket full “with water of river”. One thus obtained a paste to which, thanks to an ad hoc mould, one gave the shape of a cup.

At this point was held the delicate part of work: too much in a hurry in the mould, the paste would not have been rather porous; insufficiently pressed, it would have let pass the totality of metal tested. It was then proceeded to the desiccation of the cups on a board located near a fire; then only, their cooking intervened, in “a moderately heated” furnace.

Not exact receipt, consequently, only of the empirical councils and a dexterity which one was to transmit the secrecy of Master to disciple, if not of father out of wire.

How the Essayeur use does the cup? It takes two small samples of metal to be subjected to the experimentation (it is consequently about a destructive, impossible control on certain parts). It weighs them carefully both; it preserves some like witness and place the other in a cup which it introduces into his furnace. In order to easily be able and quickly to treat tiny quantities of metal, this furnace is low-size, approximately 20 X 50 cm, sometimes less. The tester carries the sample at his melting point after having added Plomb, in a quantity which depends on the weight and the quality supposed of metal to test (there exists for that of the tables to respect); under the effect of heat, this lead oxidizes one speaks about litharge and it carries with him copper oxide through the porous crucible. It remains at the hearth of the refining furnace only nonoxydable pure metal; once cooled, this one is weighed and its mass compared with that of the first sample. To tell the truth, which the operator employs here at ends of control, is an authentic process of refining of gold and money.

Except for some infinitesimal variation (evaporation, loss with the passage of the porous crucible), the process is reliable. However, a problem of scale remains. It is possible to practice cupellation only on silverware or the weldings (gold and copper). Indeed, if the money belongs to gold alloy poses the problem of the separation of two noble metals. They oxidize neither one nor the other and finish at the bottom of the crucible, still narrowly mixed. However precisely, the alloys of jewelry are made up thanks to hard an additional metal contribution intended to compensate for the malleability of pure gold, and to possibly reduce the cost of the part. In Venice, this contribution generally consists of a mixture of two thirds of money and of a third of copper. One cannot thus use the cup to test gold. In fact, the test is practiced only for silverware, and this is why in Venice, the controllers of the money will be traditionally called sazzadori (of sazzo).

So that this problem of separation is solved, it is necessary to wait until 1518 and the discovery of the method known as of the inquartation. The alloy remaining after cupellation is enriched by a carefully measured quantity of money, heated then subjected to the action of strong water until dissolution of all the money; it is advisable to enrich metal tested, because if the proportion of gold is too high, the acid solution is unable to attack alloy. At the end of these operations, the metal which remains is pure gold. However the money disappeared in the acid solution; for the time being it is lost. And this is why to the 12th century, Theophilus Presbyter recommends already the separation of the workshops working gold and the money, in order to prevent that two metals do not mix accidentally. Elementary precaution: it is besides as well as Zecca will proceed during all its history. In his treaty, the medieval author consigns moreover a method to refine gold by eliminating the money. Nothing astonishing with that; during the top the Middle Ages, research of the Eastern Alchimiste S enriched knowledge as regards metallurgy considerably; thus Jabir Ibn Hayyan which works at the court of caliph Haroun Al Rashid discovers, as of the 8th century, a process conveniently to manufacture the nitric acid essential to the tests.

One will manage only later to recover two metals. In fact, at the end of 18th, in the accountancy of Zecca relating to the operations of manufacture of the sequin (gold currency) a line entitled appears: money found in fusions. As for the money lost during the tests, it is recovered while immersing in the acid solution of the copper plates, on which the precipitated money comes to settle. By repeated immersions and successive washings, one obtains a dust which, treated with the Salpêtre and the Borate of soda, melted out of crucible, gives almost pure money.