[37] Molybdaena is usually hearth-lead in De Re Metallica, but the German translation in this instance uses pleyertz, lead ore. From the context it would not appear to mean hearth-lead—saturated bottoms of cupellation furnaces—for such material would not contain appreciable silver. Agricola does confuse what are obviously lead carbonates with his other molybdaena (see [note 37, p. 476]).
[Pg 401][38] The term cadmia is used in this paragraph without the usual definition. Whether it was cadmia fornacis (furnace accretions) or cadmia metallica (cobalt-arsenic-blende mixture) is uncertain. We believe it to be the former.
[39] Ramentum si lotura ex argento rudi. This expression is generally used by the author to indicate concentrates, but it is possible that in this sentence it means the tailings after washing rich silver minerals, because the treatment of the rudis silver has been already discussed above.
[40] Ustum. This might be rendered "burnt." In any event, it seems that the material is sintered.
[Pg 402][41] Aes purum sive proprius ei color insederit, sive chrysocolla vel caeruleo fuerit tinctum, et rude plumbei coloris, aut fusci, aut nigri. There are six copper minerals mentioned in this sentence, and from our study of Agricola's De Natura Fossilium we hazard the following:—Proprius ei color insederit,—"its own colour,"—probably cuprite or "ruby copper." Tinctum chrysocolla—partly the modern mineral of that name and partly malachite. Tinctum caeruleo, partly azurite and partly other blue copper minerals. Rude plumbei coloris,—"lead coloured,"—was certainly chalcocite (copper glance). We are uncertain of fusci aut nigri, but they were probably alteration products. For further discussion see note on p. [109].
[42] Historical Note on Copper Smelting.—The discoverer of the reduction of copper by fusion, and his method, like the discoverer of tin and iron, will never be known, because he lived long before humanity began to make records of its discoveries and doings. Moreover, as different races passed independently and at different times through the so-called "Bronze Age," there may have been several independent discoverers. Upon the metallurgy of pre-historic man we have some evidence in the many "founders' hoards" or "smelters' hoards" of the Bronze Age which have been found, and they indicate a simple shallow pit in the ground into which the ore was placed, underlaid with charcoal. Rude round copper cakes eight to ten inches in diameter resulted from the cooling of the metal in the bottom of the pit. Analyses of such Bronze Age copper by Professor Gowland and others show a small percentage of sulphur, and this is possible only by smelting oxidized ores. Copper objects appear in the pre-historic remains in Egypt, are common throughout the first three dynasties, and bronze articles have been found as early as the IV Dynasty (from 3800 to 4700 B.C., according to the authority adopted). The question of the origin of this bronze, whether from ores containing copper and tin or by alloying the two metals, is one of wide difference of opinion, and we further discuss the question in [note 53, p. 411], under Tin. It is also interesting to note that the crucible is the emblem of copper in the hieroglyphics. The earliest source of Egyptian copper was probably the Sinai Peninsula, where there are reliefs as early as Seneferu (about 3700 B.C.), indicating that he worked the copper mines. Various other evidences exist of active copper mining prior to 2500 B.C. (Petrie, Researches in Sinai, London, 1906, p. 51, etc.). The finding of crucibles here would indicate some form of refining. Our knowledge of Egyptian copper metallurgy is limited to deductions from their products, to a few pictures of crude furnaces and bellows, and to the minor remains on the Sinai Peninsula; none of the pictures were, so far as we are aware, prior to 2300 B.C., but they indicate a considerable advance over the crude hearth, for they depict small furnaces with forced draught—first a blow-pipe, and in the XVIII Dynasty (about 1500 B.C.) the bellows appear. Many copper articles have been found scattered over the Eastern Mediterranean and Asia Minor of pre-Mycenaean Age, some probably as early as 3000 B.C. This metal is mentioned in the "Tribute of Yü" in the Shoo King (2500 B.C.?); but even less is known of early Chinese metallurgy than of the Egyptian. The remains of Mycenaean, Phoenician, Babylonian, and Assyrian civilizations, stretching over the period from 1800 to 500 B.C., have yielded endless copper and bronze objects, the former of considerable purity, and the latter a fairly constant proportion of from 10% to 14% tin. The copper supply of the pre-Roman world seems to have come largely, first from Sinai, and later from Cyprus, and from the latter comes our word copper, by way of the Romans shortening aes cyprium (Cyprian copper) to cuprum. Research in this island shows that it produced copper from 3000 B.C., and largely because of its copper it passed successively under the domination of the Egyptians, Assyrians, Phoenicians, Greeks, Persians, and Romans. The bronze objects found in Cyprus show 2% to 10% of tin, although tin does not, so far as modern research goes, occur on that island. There can be no doubt that the Greeks obtained their metallurgy from the Egyptians, either direct or second-hand—possibly through Mycenae or Phoenicia. Their metallurgical gods and the tradition of Cadmus indicate this much.
By way of literary evidences, the following lines from Homer (Iliad, XVIII.) have interest as being the first preserved description in any language of a metallurgical work. Hephaestus was much interrupted by Thetis, who came to secure a shield for Achilles, and whose general conversation we therefore largely omit. We adopt Pope's translation:—
There the lame architect the goddess found
Obscure in smoke, his forges flaming round,
While bathed in sweat from fire to fire he flew;
[Pg 403]And puffing loud the roaring bellows blew.
* * *
In moulds prepared, the glowing ore (metal?) he pours.
* * *
"Vouchsafe, oh Thetis! at our board to share
The genial rites and hospitable fare;
While I the labours of the forge forego,
And bid the roaring bellows cease to blow."
Then from his anvil the lame artist rose;
Wide with distorted legs oblique he goes,
And stills the bellows, and (in order laid)
Locks in their chests his instruments of trade;
Then with a sponge, the sooty workman dress'd
His brawny arms embrown'd and hairy breast.
* * *
Thus having said, the father of the fires
To the black labours of his forge retires.
Soon as he bade them blow the bellows turn'd
Their iron mouths; and where the furnace burn'd
Resounding breathed: at once the blast expires,
And twenty forges catch at once the fires;
Just as the God directs, now loud, now low,
They raise a tempest, or they gently blow;
In hissing flames huge silver bars are roll'd,
And stubborn brass (copper?) and tin, and solid gold;
Before, deep fixed, the eternal anvils stand.
The ponderous hammer loads his better hand;
His left with tongs turns the vex'd metal round.
And thick, strong strokes, the doubling vaults rebound
Then first he formed the immense and solid shield;
Even if we place the siege of Troy at any of the various dates from 1350 to 1100 B.C., it does not follow that the epic received its final form for many centuries later, probably 900-800 B.C.; and the experience of the race in metallurgy at a much later period than Troy may have been drawn upon to fill in details. It is possible to fill a volume with indirect allusion to metallurgical facts and to the origins of the art, from Greek mythology, from Greek poetry, from the works of the grammarians, and from the Bible. But they are of no more technical value than the metaphors from our own tongue. Greek literature in general is singularly lacking in metallurgical description of technical value, and it is not until Dioscorides (1st Century A.D.) that anything of much importance can be adduced. Aristotle, however, does make an interesting reference to what may be brass (see note on p. [410]), and there can be no doubt that if we had the lost work of Aristotle's successor, Theophrastus (372-288 B.C.), on metals we should be in possession of the first adequate work on metallurgy. As it is, we find the green and blue copper minerals from Cyprus mentioned in his "Stones." And this is the first mention of any particular copper ore. He also mentions (XIX.) pyrites "which melt," but whether it was a copper variety cannot be determined. Theophrastus further describes the making of verdigris (see [note 4, p. 440]). From Dioscorides we get a good deal of light on copper treatment, but as his objective was to describe medicinal preparations, the information is very indirect. He states (V, 100) that "pyrites is a stone from which copper is made." He mentions chalcitis (copper sulphide, see note on, p. [573]); while his misy, sory, melanteria, caeruleum, and chrysocolla were all oxidation copper or iron minerals. (See notes on p. [573].) In giving a method of securing pompholyx (zinc oxide), "the soot flies up when the copper refiners sprinkle powdered cadmia over the molten metal" (see [note 26, p. 394]); he indirectly gives us the first definite indication of making brass, and further gives some details as to the furnaces there employed, which embraced bellows and dust chambers. In describing the making of flowers of copper (see [note 26, p. 538]) he states that in refining copper, when the "molten metal flows through its tube into a receptacle, the workmen [Pg 404]pour cold water on it, the copper spits and throws off the flowers." He gives the first description of vitriol (see [note 11, p. 572]), and describes the pieces as "shaped like dice which stick together in bunches like grapes." Altogether, from Dioscorides we learn for the first time of copper made from sulphide ores, and of the recovery of zinc oxides from furnace fumes; and he gives us the first certain description of making brass, and finally the first notice of blue vitriol.
The next author we have who gives any technical detail of copper work is Pliny (23-79 A.D.), and while his statements carry us a little further than Dioscorides, they are not as complete as the same number of words could have afforded had he ever had practical contact with the subject, and one is driven to the conclusion that he was not himself much of a metallurgist. Pliny indicates that copper ores were obtained from veins by underground mining. He gives the same minerals as Dioscorides, but is a good deal confused over chrysocolla and chalcitis. He gives no description of the shapes of furnaces, but frequently mentions the bellows, and speaks of the cadmia and pompholyx which adhered to the walls and arches of the furnaces. He has nothing to say as to whether fluxes are used or not. As to fuel, he says (XXXIII, 30) that "for smelting copper and iron pine wood is the best." The following (XXXIV, 20) is of the greatest interest on the subject:—"Cyprian copper is known as coronarium and regulare; both are ductile.... In other mines are made that known as regulare and caldarium. These differ, because the caldarium is only melted, and is brittle to the hammer; whereas the regulare is malleable or ductile. All Cyprian copper is this latter kind. But in other mines with care the difference can be eliminated from caldarium, the impurities being carefully purged away by smelting with fire, it is made into regulare. Among the remaining kinds of copper the best is that of Campania, which is most esteemed for vessels and utensils. This kind is made in several ways. At Capua it is melted with wood, not with charcoal, after which it is sprinkled with water and washed through an oak sieve. After it is melted a number of times Spanish plumbum argentum (probably pewter) is added to it in proportion of ten pounds of the lead to one hundred pounds of copper, and thereby it is made pliable and assumes that pleasing colour which in other kinds of copper is effected by oil and the sun. In many parts of the Italian provinces they make a similar kind of metal; but there they add eight pounds of lead, and it is re-melted over charcoal because of the scarcity of wood. Very different is the method carried on in Gaul, particularly where the ore is smelted between red hot stones, for this burns the metal and renders it black and brittle. Moreover, it is re-melted only a single time, whereas the oftener this operation is repeated the better the quality becomes. It is well to remark that all copper fuses best when the weather is intensely cold." The red hot stones in Gaul were probably as much figments of imagination as was the assumption of one commentator that they were a reverberatory furnace. Apart from the above, Pliny says nothing very direct on refining copper. It is obvious that more than one melting was practised, but that anything was known of the nature of oxidation by a blast and reduction by poling is uncertain. We produce the three following statements in connection with some bye-products used for medicinal purposes, which at least indicate operations subsequent to the original melting. As to whether they represent this species of refining or not, we leave it to the metallurgical profession (XXXIV, 24):—"The flowers of copper are used in medicine; they are made by fusing copper and moving it to another furnace, where the rapid blast separates it into a thousand particles, which are called flowers. These scales are also made when the copper cakes are cooled in water (XXXIV, 35). Smega is prepared in the copper works; when the metal is melted and thoroughly smelted charcoal is added to it and gradually kindled; after this, being blown upon by a powerful bellows, it spits out, as it were, copper chaff (XXXIV, 37). There is another product of these works easily distinguished from smega, which the Greeks call diphrygum. This substance has three different origins.... A third way of making it is from the residues which fall to the bottom in copper furnaces. The difference between the different substances (in the furnace) is that the copper itself flows into a receiver; the slag makes its escape from the furnace; the flowers float on the top (of the copper?), and the diphrygum remains behind. Some say that in the furnace there are certain masses of stone which, being smelted, become soldered together, and that the copper fuses around it, the mass not becoming liquid unless it is transferred to another furnace. It thus forms a sort of knot, as it were, in the metal."