An Encyclopedia of the History of Technology

Ian McNeil

• Publisher: Routledge
• Year: 2002
• Print ISBN:
  9780415013062
• eBook ISBN:
  9781134981649
• Topic: History
• Subtopic: World History
• Index: History

* 22 sections cover the entire field of the history of technology and each section summarises the development of its subject from the earliest times to the present day * Written without unnecessary jargon * 2 extensive indexes of Names and Topics * Usefully illustrated with 150 black & white photographs and line drawings to explain key advances `Contain[s] a vast amount of reliable information over a very wide field. It is certainly a work of which I shall myself make frequent use ... it deserves to find a place ... in every reference library.' - Times Higher Education Supplement `The coverage is excellent ... a most valuable single-volume source which for its comprehensiveness and ease of reference will earn its place in both specialist and general reference collections.' - Reference Reviews `Informative and comprehensive, remarkable in its coverage ... covers every aspect of technology from the Stone Age to the Space Age ... will undoubtedly help readers to get a grip on and feel of an enormous range of subjects ... An invaluable and practical addition to most office bookshelves or libraries.' - New Civil Engineer `The authors represented in this book are to be congratulated for their readable and reliable surveys of the past and present status of the major areas where mankind has harnessed science for the production of useful products and processes.' - Choice

PART ONE

MATERIALS

1

NON-FERROUS METALS

A.S.DARLING

NEOLITHIC ORIGINS

The birth of metallurgy is shrouded in obscurity, although weathered crystals of native copper might well have attracted the attention of ancient man because of their remarkable green colouration. Beneath this superficial patina copper in metallic form would have been discovered. Decorative and practical applications would undoubtedly have been sought for this relatively hard, heavy material, and primitive man would have been most impressed by the malleability of copper, which allowed it, unlike wood and stone, to be hammered into a variety of useful shapes.

The sharp distinction between the brightness, lustre and ductility of the interior of a crystal of native copper and the brittleness and stonelike characteristics of the g reen patina with which it was encrusted, would also have been noted. From this, the first users of metal might have concluded that all non-living primordial matter had originally been in this pure, bright, noble and amenable metallic state, although it had, like human beings, a natural tendency to fall from grace and, by contact with nature and the passage of time, to assume a degraded form.

Differing conclusions can, however, be drawn from the same set of evidence, and some of the earliest metallurgists, it appears, favoured a more optimistic interpretation which suggested that the natural tendency of most metals was towards rather than away from perfection. This tendency was encouraged by contact with nature so that metals buried deep in the bowels of the earth tended to mature and improve. Silver, according to this interpretation, was regarded as an unripened form of gold.

COPPER

Cold forging of native copper

The archaeological evidence indicates that although lead was also known at a very early date, the first metal to be practically utilized was copper. Small beads and pins of hammered copper found at Ali Kosh in Western Iran and Cayönü Tepesi in Anatolia date from the period between the 9th and 7th millennia BC and were made from native, unmelted copper. During the later stages of the Neolithic period more significant metallurgical developments appear to have originated in the mountainous regions north of the alluvial plains where the civilizations of the Tigris and Euphrates subsequently developed. Much use was then made of native copper which was hammered directly into small articles of jewellery or of ritual significance. At a later stage larger artefacts such as axe-heads were made by melting together native crystals of copper in a crucible and casting the molten metal to the required shape. Finally, however, copper was extracted from its ores by pyrometallurgical methods.

The period during which copper was known to Neolithic man but not extensively employed is known as the Chalcolithic Age. The beginning of the Copper Age is associated with the emergence of smelting processes which allowed copper to be extracted from its ores. Native copper must undoubtedly have been worked in sites which were close to the outcrops where the metals had been found. It seems logical to assume, therefore, that copper ores were first reduced to metal, quite fortuitously, in the fires where native crystals were annealed at temperatures well below their melting point to soften them after cold forging, or in the furnaces where crystals were melted together.

Apart from gold, silver and the other noble metals, copper is the only metal which is found as native crystals in metallic form. This is because its affinity for oxygen is lower than that of most other common metals, and as a result native crystals, although not always abundant, can usually be found in weathered out-crops of copper ore.

The native copper which is still abundantly available in the vicinity of the Lake Superior deposits in North America, was worked from 3000 BC until shortly after the arrival of the Spanish invaders by the North American Indian: Giovanni Verazzano, who visited the Atlantic Coast in 1524, commented upon the vast quantities of copper owned by the Indians, and in 1609 Henry Hudson found them using copper tobacco pipes. Although unaware that copper could be melted and cast, they were working large lumps into weapons and jewellery.

The burial mounds of the pre-Columbian Indians of the Ohio valley contained many copper implements such as adzes, chisels and axes, which from their chemical composition appear to have been made from Lake Superior copper (see Figure 1.1). In more recent times the Indians on the White River in Alaska used caribou picks to dig copper nuggets out of alluvial gravels. Eskimos living in the Coppermine district on the Arctic shore of Coronation Gulf were using native

Figure 1.1: Adze blade from an unmelted nugget of native copper forged by preColumban Indians of the Ohio Valley Hopewell culture. Found in a burial mound at Mound City, Ohio, USA. Date 200 BC–AD 600. Note how internal flaws in the nugget have spread to the surface and failed to weld during forging.
Courtesy of the British Museum Laboratory.

copper as late as 1930, when it was reported that nuggets were occasionally found which were large enough to forge into knives with 20cm (8in) blades.

The implements and weapons produced in North America from native copper all appear to have been produced by cold forging with frequent annealing at temperatures below 800°C. After an approximation to the final shape had been obtained in this way, the articles were finished by cold working. The cutting edges were hardened as much as possible by local hammering, and the craftsmen who produced these artefacts were obviously well aware that copper could be hardened by deformation and softened by annealing. It is difficult to understand, however, why they never succeeded in melting copper.

In Asia Minor, however, where copper was far less accessible, metallurgical development was very rapid. Cities and civilizations, which produce both wealth and demand, seem far more effective than natural resources in stimulating successful technical innovation.

Melted and cast native copper

Most of the larger copper artefacts produced in the Middle East between the seventh and fourth millennia BC have a micro-structure which is far from uniform. It consists of crystals which appear to have grown from the melt by throwing out arms into the surrounding liquid. From these arms secondary branches and spines have grown, thus producing a ‘dendritic’ structure characteristic of cast metal. Because of this structure, and their generally high purity, such articles could have been produced only by melting together crystals of native copper. This technique marks a great step forward, although the evidence available is very limited and it cannot be said when copper was first melted or even when the first attempts were made to utilize the effect in a practical manner. During the long period when native copper was being worked and annealed, some of the smaller crystals would, inevitably, have been accidently melted. The early coppersmiths would have attempted, instinctively, to avoid such unfortunate accidents, and would soon have developed an appreciation and recognition of those fiery conditions which would encourage copper to renounce the solid state and become mobile.

It seems most probable that when native copper was first intentionally melted it would have been heated from above by a heaped charcoal fire, and encouraged to run together and form a lens-like ingot in a clay-lined saucer-shaped depression in the ground immediately beneath the fuel bed. This arrangement might possibly have required forced draught, from bellows, to attain the temperatures required, although with suitable chimney arrangements this may not have been essential.

Crucible furnaces must soon have been employed, however, to produce items such as flat axes or mace heads which were cast directly to size. The earliest crucible furnace remains so far identified were found at Abu Matar, near the old city of Beersheba in Israel on a site used between 3300 and 3000 BC (see Figure 1.2). These furnaces appear to have had a vertical cylindrical clay shaft, supported in such a way that air could enter freely at the lower end, providing the necessary draught. The hemispherical clay crucible, about 10cm in diameter, was supported about half-way up the shaft by charcoal packed into the base of the furnace.

The slags produced by such melting processes appear, in general, to be far more enduring than the furnaces themselves. The earliest vitrified copper-bearing slags were found at Catal Huyük in Anatolia at a site dating from 7000–6000 BC, where specimens of beads and wire which appear to have been made from native copper were found. The first copper artefacts which, from their purity, appear almost certainly to have been produced by forging melted and cast native copper were found at Sialk in Iran, at a site dated around 4500 BC. These contained substantial quantities of copper oxide, and from their microstructure appeared, after casting, to have been either hot forged or cold worked and annealed. The earliest Egyptian artefacts produced from cast and wrought native copper appear to date from the period between 5000 and 4000 BC.

The archaeological evidence suggests that the technique of melting and casting native copper originated in Anatolia, and between 5000 and 4000 BC spread rapidly over much of the Middle East and Mediterranean area. Three

Figure 1.2: A reconstruction based on the remains of the earliest known crucible furnace, dating from 3300–3000 BC, found at the Chalcolithic site at Abu Matar, near Beersheba, excavated by J.Perrot in 1951. This appears to have been a natural draught furnace used for remelting impure copper in a hemispherical crucible which was supported on and immersed in a bed of charcoal halfway up the furnace shaft.
After J.Perrot.

flat axes produced by this approach were found between 1908 and 1961 in the Eneolithic Italian sepulchral cave Bocca Lorenza, close to Vicenza. Because of their high purity, these axes can be clearly distinguished from artefacts produced from smelted copper.

Smelting of oxide and carbonate copper ores

It seems that towards the end of the fourth millennium BC, the supplies of native copper accessible to the ancient world were incapable of satisfying a rapidly increasing demand. Most of the copper artefacts produced after 3500 BC contain substantial quantities of nickel, arsenic, iron, or other base metal impurities which indicates that they had been produced from copper which had been extracted from ore. Systematic copper mining was being undertaken well before this time, however, as early as the first half of the sixth millennium.

The Copper Age began when improved copper extraction techniques meant that primitive copper workers were no longer dependent upon supplies of relatively pure native metal. The rate of this transformation increased rapidly soon after the establishment of the Tigris and Euphrates civilizations. The wealth and specialized demand provided by these urban societies must have stimulated early copper workers to prospect in the northern mountainous regions where weathered outcrops of copper were most likely to be encountered.

The earliest copper workers appear to have extracted their metal from oxide or carbonate ores which, although not always rich or plentiful, could generally be smelted successfully in the primitive furnaces then available. The early smelters all appeared to understand instinctively that charcoal fires could be adjusted to provide atmospheric conditions which simultaneously reduced copper and oxidized iron. Methods were thus evolved which allowed relatively pure copper to be separated in the molten state from iron and other unwanted materials in the ore. These, when suitably oxidized, could be induced to dissolve in the slag. The primary ores of copper are invariably complex sulphides of copper and iron, and are generally disseminated in a porous rock such as sandstone which rarely contains more than 2 per cent by weight of copper. Such deposits were too lean to be exploited by primitive man, who sought for the richer if more limited deposits produced by the weathering and oxidation of primary ores. Thus, at Rudna Glava in Yugoslavia, a copper mine worked in the 6th millennia, did not exploit the main chalcopyrite ore body, but worked instead a thin, rich carbonate vein produced by leaching and weathering. This concentrated ore contained 32 per cent of copper and 26 per cent of iron. Quartz sand would have been added to such a smelting charge to ensure that most of the iron separated into the slag.

At Timna, in the southern Negev, copper has been mined and smelted since the dawn of history. Extensive workings, slag heaps and furnaces have remained with little disturbance since Chalcolithic, Iron Age and Roman times. These mines, traditionally associated with King Solomon, were in fact worked by the Egyptian Pharaohs during much of the Iron Age until 1156 BC.

The primary ore deposit at Timna is based on the mineral chrysocolla and is currently being exploited on a large scale. Since this ore contains only about 2 per cent of copper, it could not have been effectively smelted in ancient times. During the Chalcolithic or historical periods copper was extracted at Timna from sandstone nodules in the Middle White sandstone beds overlying the chrysocolla deposits. The nodules contain between 6 and 37 per cent of copper, which exists as the minerals malachite, azurite and cuprite. The remainder is largely silica, and the nodules contain little iron. In the fourth millennium BC copper was extracted from them in furnaces: a rough hole in stony ground, approximately 30cm (1ft) in diameter, was surrounded by a rudimentary stone wall to contain the charge, which consisted of crushed ore mixed with charcoal from the desert acacia. Controlled quantities of the crushed iron oxide haematite, was added to the charge as a flux, to reduce the

Figure 1.3: Reconstructions based on the remains of smelting furnaces used (a) in the twelfth century BC, and (b) in the eleventh century BC, at the ancient copper smelting site of Timna in the Southern Negev region of Israel.
Courtesy of the Institute of Metals.

melting point of the silicious material and improve the separation between the copper and the slag.

The Chalcolithic smelting furnaces at Timna appeared to have had no tap hole and no copper ingots were found. High concentrations of prills and blebs of metallic copper were found in the slag, however, and it seems possible that the metal never, in fact, separated from the slag in massive form: after smelting the slag would have been broken up to remove the prills which were then remelted together in a crucible furnace.

A more highly developed smelting furnace used by the Egyptians at Timna around 1200 BC is shown in Figure 1.3 (a). The slags from such furnaces contained up to 14 per cent of lime which was added to the charge as crushed calcareous shells from the Red Sea. This addition would have improved slag metal separation and allowed the reduced copper to settle to the bottom of the furnace and to solidify below the slag as plano-convex ingots.

Smelting techniques appeared to have reached their zenith at Timna around 1100 BC. After the smelting operation the slag and metal appear to have been tapped simultaneously from the furnace into a bed of sand where, as recent simulation experiments by Bamberger have shown, they would have remained liquid for about fifteen minutes, providing ample time for the molten copper to sink beneath the slag to form well-shaped ingots about 9cm (3.5in) in diameter. For Bamberger' reconstruction see Figure 1.3 (b).

The rings and other small artefacts of iron found at Timna are now thought to have been by-products of the main copper refining operation. Lead isotope ‘finger-printing’ has shown that the source of the iron was the haematite used to flux the copper ore during refining. It would appear that when the ‘as smelted’ copper was remelted in a crucible furnace in preparation for the casting of axes and other artefacts, any surplus iron it contained separated at the surface of the melt to form a sponge-like mass permeated by molten copper. This layer would, in all probability, have been skimmed from the surface of the melt before it was poured. At a later stage it must have been found that the iron/copper residue could be consolidated by hot forging and worked to the shape required. The presence of copper is known to improve the consolidation of iron powder, and it would seem, therefore, that a sophisticated powder metallurgical process, utilizing liquid phase bonding, was being operated at Timna in Iron Age times.

Smelting of sulphide copper ores

From the presence of arsenic and other impurities in many of the early Copper Age artefacts it must be concluded that much of the copper used was extracted from sulphide rather than oxide or carbonate ores. In prehistory, as in modern times, the bulk of the world' supply of copper appears to have been obtained from ores based on chalcopyrite, a mixed sulphide containing equi-atomic proportions of iron and copper. Chalcopyrite must be roasted in air to convert it to a mixture of iron and copper oxides before it can be smelted. Moreover, because chalcopyrite ores contain in general less than 2 per cent of copper, and because of the presence of large quantities of unwanted earthy material, they do not respond to simple smelting processes.

The sulphide copper ores exploited at the beginning of the Copper Age appear to have been thin, localized and very rich deposits which lay some distance below the surface of a weathered and oxidized primary outcrop. Although the presence of such enrichment zones has been recognized by mining engineers and geologists for many years, their significance as ancient sources of copper has only recently been fully appreciated.

Due to the atmospheric oxidation which occurs at the surface of chalcopyrite outcrops, the sulphides are partially converted to more ...

Table of contents

• Cover
• Half Title Page
• Title Page
• Copyright Page
• Table of Contents
• Preface
• Dedication
• Introduction: Basic Tools, Devices and Mechanisms
• PART ONE: MATERIALS
• PART TWO: POWER AND ENGINEERING
• PART THREE: TRANSPORT
• PART FOUR: COMMUNICATION AND CALCULATION
• PART FIVE: TECHNOLOGY AND SOCIETY
• The Contributors
• Index of Names
• Index of Topics