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The paper entitled "Some Metallurgical Processes of the Early Sixteenth Century (1530)" by F Sherwood Taylor, is published in the Transactions of the Newcomen Society, 1953-54 Vol 29.
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Alchemy has always been distinct from metallurgy. At all periods since at least the first century AD, there have been on the one hand men and women who were trying to transmute base metals into gold; and on the other hand practical goldsmiths and fine metal-workers carrying on their craft under no illusion that they could make gold or silver, though they were well able to imitate it. These metal-workers often compiled manuscripts books of workshop-recipes, some of which have survived; their tone is that of the workshop-recipe of today, dry, precise, free from any literary pretension, and quite different from the works of the alchemists. It seems, however, that alchemists occasionally got possession of these metal-workers' recipes, and surrounding them with a high-sounding introduction, served them up as alchemical secrets.
The author of this paper describes "a very curious book of great rarity and known to few", the Voarchadumia of Giovanni Agostino Pantheo, published in 1530 at Venice. This book contains eleven superb plates illustrating current metallurgical practices, also interesting practical recipes - amongst all the obscure alchemical material.
"The central theme is the cementation process for the purification of gold. This ancient process consists in essence of beating out gold into thin plates or leaves of the thickness of paper and forming a pile, consisting of these leaves alternating with layers of some mixture that when heated evolves what we now know to be acid gases, normally hydrogen chloride. The acid-producing material, when fired in a crucible, attacked the baser metals which were alloyed with the gold, producing soluble salts, but did not attack the gold itself; these salts could be scraped or dissolved from the gold."
The recipe, as 'written up' by Pantheo:
"How Voarchadumia itself is done. Of leaves of gold (proportioned as below) and of ground salt as much, let one measure be taken. Of burned and finely powdered clay, two parts. Let the salt and clay be sifted in a sieve. And having mixed layer upon layer they are cemented in unglazed pots, and in a reverbatory furnace. Note that every cementation... required each time 24 hours of firing, namely nine in augmentation, nine in fixation and finally six in alteration"Pantheo then explains that the cementation does not destroy the gold. It takes away half a grain from 24 carats, but this is not gold. This may indicate that the purest gold then known still contained some alloy. He tells us that in fact the cementation makes the gold heavier because the salt enters it by the fusion of the fire, but this can be removed by boiling with water. After the cementation the material is fused and the salt and slag poured off from the gold.
The Voarchadumia also contains probably the earliest known illustration of coining processes:
The plate on the left shows a metal fillet or strip being drawn by the aid of a pair of rollers through a rectangular aperture in a draw-plate. The plate on the right shows the cutting process. The use of a draw-plate in preparing strip for coining is mentioned by Leonardo da Vinci, who says of the cutting-press:
"It can also be made without a spring. But the screw above must always be joined to the part of the moveable sheath... a coin must before all be made perfect in weight and size and thickness. Therefore have several plates of metal made of the same size and thickness all drawn through the same gauge so as to come out in strips. And out of these strips you will stamp the coins quite round..."Leonardo's drawing does not show either strip or the main part of the press, but presumably the process he describes is similar to that of Pantheo. He also sketched a drawbench for making mirrors which may suggest that he was familiar with its use for making flat strip. Drawbenches are mentioned as in use in the French Mint of 1552. The Royal Mint seems to have used this method up to the beginning of the nineteenth century but then to have replaced the draw-plate by a pair of fixed steel cylinders: after 1908 drawing was superseded by rolling.
Pantheo passes to simple transcription of metallurgical recipes of some interest. This one is for 'brittle metallic mirrors':
"Three parts of copper are mixed with one of tin by a second fusion in the blast furnace, and thin plates are cast by means of a flat stone and a cover both of limestone, one lying on the other. Then the plates are made of equal measure by cutting off what is superfluous with a knife, and are smoothed longways and crossways, first with medium emery and then with fine until it is dry, having first of all been stuck on to a board with raw gypsum and water. Afterwards they are polished on a rough linen cloth or a household leather with sponthia or tripoli and white lead or tutty powder, first sprinkled with oil. Then they are rubbed with the palms of the hand, made bright and boxed up and kept ".
The complete text of this paper can be purchased on line from our archive.
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