The research results were published in the Journal of Archaeological Science. Journal Reference : M. Rehren, S. Farid, E. Pernicka, D. ScienceDaily, 1 September Metallurgy likely has more than one birthplace. The oxygen from the air combines with some of the iron to produce iron oxide which reacts with the carbon in the pig iron to produce carbon monoxide which releases some of the carbon from the pig iron.
The remaining carbon is removed when the oxygen in the air is combined with silicon and manganese which form a slag. The resulting metal was brittle so manganese is added to remove the brittleness and then carbon is added to bring the steel up to the desired carbon content. The same process was independently invented in America by William Kelly.
An alternative method of making steel, known as the open-hearth process was invented in by William and Frederick Siemens and then improved by Pierre and Emile Martin. The open—hearth process involved pre-heating the air going into the furnace in two chambers that operated alternatively.
The chambers, known as regenerators, contained a fire brick checker work and were alternatively heated by the furnace gases so the air passing into the furnace through the regenerators was heated resulting in higher furnace temperatures.
As with the Bessemer process, iron oxide was used to remove carbon and other impurities, and manganese was added to remove brittleness and if necessary carbon was added to obtain the desired carbon levels. The invention of electrical generators led to the use of electricity for heating furnaces. The first electric arc furnace began operation in and, while more expensive than the Bessemer and the open-hearth processes, was able to produce better quality steel due to it having fewer impurities than steel which had been in contact with fuel.
Electric furnaces were able to produce greater heat and the temperatures could be more easily controlled than with ordinary furnaces. The use of electric furnaces was to result in the large scale production of metals such as tungsten, chromium and manganese which when added to steel gave it useful properties such as improved hardness and resistance to wear.
The electric furnace also allowed the mass production of aluminum. Aluminum is widespread on the Earth but it was difficult and expensive to extract from its ore, bauxite, before the invention of the electric furnace. The electric furnace produces aluminum by a process of high temperature electrolysis which produces molten aluminum in large quantities, although the process uses substantial quantities of electricity. It had been long recognized that the use of oxygen, rather than air, in steel making would produce higher temperatures, faster production and reduce fuel costs.
The high cost of producing oxygen stopped its use in steel making, until the price fell substantially and in the L-D process for using oxygen in steel making was developed. The L-D process involves blowing a jet of nearly pure oxygen at supersonic speed on to the surface of molten iron. The oxygen quickly burns out the carbon and other impurities resulting in faster production and reduced fuel costs.
The social and cultural consequences of the discovery of metallurgy were initially quite minor. Copper was initially used mainly for ornaments and jewelry as it was too soft a material to replace the stone tools and weapons used in Neolithic times. It was only when bronze was invented that metal tools and weapons replaced stone tools and weapons to create a Bronze Age.
Bronze however was a reasonably expensive metal and when iron smelting was discovered by the Hittites the new metal soon replaced bronze as the principal material for tools and weapons.
Iron ores are reasonably widespread and iron is a harder material than bronze, making it better for both tools and weapons. Iron was used for a wide variety of purposes such as nails and tools, cooking pots and kitchen utensils, axes for clearing land and for the tips of ploughs. The use of iron tools and weapons gave humankind greater control of their environment leading to increased population and larger settlements.
Iron became the principal material for the Industrial Revolution being used in steam engines, industrial machinery, in railways for rails and locomotives, for bridges, buildings and in iron ships. The Bessemer and open-hearth steel making processes led to a great reduction in the price and increase in production of steel. Cheap steel replaced iron in a great variety of applications.
Steel was used in railways and for ships and in bridge building. Motor vehicles became one of the biggest users of steel in the 20th century and different types of steel began to be developed for different purposes. Cutting tools were made from steel containing chromium and tungsten as that steel remains hard even at high temperatures.
Excavating machinery was made from wear resistant manganese steels and transformers, generators and motors were made from silicon steel due to its magnetic quality. Stainless steel containing chromium and nickel was widely used in kitchens and in industrial plants vulnerable to corrosion as it does not rust.
Steel coated in zinc or tin also resists rust and is used for cans containing food and for equipment used around the home. Metallurgy has had a great effect on human societies, certainly since the Bronze Age and increasingly since the Iron Age and particularly with the modern Steel Age where a vast range of products and structures contain metals. If metals did not exist at all then we would be restricted to stone, bone and wood tools. This would have had an enormous effect on human history. It is doubtful whether the Industrial Revolution and the industrial world that emerged from it, would have been possible without metals.
It is hard to conceive of wooden or stone steam engines or internal combustion engines. Wooden engines would catch fire while it is doubtful that stone could be worked in a way that could create pistons and cylinders. Without metals it is doubtful that there would be usable electricity, as the transfer of electricity over significant distances would be difficult or impossible.
Even if there were metals, the properties of those metals would have had a major effect on human history. If the smelting and melting points of metals were different then human history would have been different.
This can be seen by the use of counter-factuals. The extensive deposits of copper on Cyprus bring the island much wealth from about BC Cyprus , in Latin, gives copper its name - cyprium corrupted to cuprum. Later, when the much scarcer commodity of tin is required to make bronze, even distant Cornwall becomes - by the first millennium BC - a major supplier of the needs of Bronze Age Europe.
The next great development in metallurgy involves a metal which is the most abundant in the earth's surface but which is much more difficult to work than copper or tin.
It is iron, with a melting point too high for primitive furnaces to extract it in pure form from its ore. The best that can be achieved is a cluster of globules of iron mixed with sludgy impurities.
This unpromising substance can be turned into a useful metal by repeated heating and hammering, until the impurities are literally forced out. A few iron objects dating from before BC have been found beads, a ring, some blades , but it is not until about BC that the working of iron is done anywhere on a regular basis. The Hittites are the first people to work iron, in Anatolia from about BC. In its simple form iron is less hard than bronze, and therefore of less use as a weapon, but it seems to have had an immediate appeal - perhaps as the latest achievement of technology with the mysterious quality of being changeable, through heating and hammering , or from a certain intrinsic magic it is the metal in meteorites, which fall from the sky.
Quite how much value is attached to iron can be judged from a famous letter of about BC, written by a Hittite king to accompany an iron dagger-blade which he is sending to a fellow monarch see Letter from a Hittite king. The discovery of steel: 11th century BC.
By the 11th century BC it has been discovered that iron can be much improved. If it is reheated in a furnace with charcoal containing carbon , some of the carbon is transferred to the iron.
This process hardens the metal; and the effect is considerably greater if the hot metal is rapidly reduced in temperature, usually achieved by quenching it in water. The new material is steel. It can be worked or 'wrought' just like softer iron, and it will keep a finer edge, capable of being honed to sharpness.
Gradually, from the 11th century onwards, steel replaces bronze weapons in the Middle East, birthplace of the Iron Age. It becomes essential, from now on, to have a good steel blade rather than a soft and indifferent one. Glass was also stored in ingots and then melted and cast in molds as needed, separating the sometimes secret process of glass creation from that of glass working.
The picture here shows glass ingots tinted with traces of copper, cobalt, and manganese. Smelting is the basic process by which one produces workable metal from metal ores. This can be done directly with copper oxide ores. Copper sulphide ores are heated in contact with air first. At this temperature the metal, now liquid, flows to the bottom of the furnace, and the remaining matter slag floats to the top, whence it is removed.
Slag usually includes large amounts of silicon and related material and produces waste heaps of glass-like or cinder-like material. Although this sounds straightforward, in antiquity, and especially before the invention of a bellows, it was difficult to attain the necessary temperature, and the extraction of copper from slag was in fact a difficult, messy, and extremely labor-intensive project.
Click for pictures. Smelting produces a blob of metal called bloom prepared for the next step. In the case of copper, that step is often casting. Iron has a higher melting point than copper. But below its melting point iron can still become spongy and amenable to treatment by hot hammering forging , which helps to extract some of the remaining impurities. Softer metals, including copper and bronze, can be shaped through cold hammering, especially after they have been smelted to remove impurities.
Because hammering is harmful to the crystalline structure, hammered metal becomes more brittle. The crystalline structure can be "reset" by annealing , a process of successive heating and slow cooling, described below. Forging iron, which is much harder than copper, requires that the bloom be reheated until it is red.
It is then hammered on an anvil, a process that physically drives out the various impurities usually silica that remain from the smelting.
Repeated heating and hammering produces ever purer and stronger iron. At the same time, since the iron is slightly malleable when it is red hot, the smith is able to shape the iron into desired forms. Annealing is the process of reheating cast or hammered metal slowly until it is red hot. This restores its crystalline structure and is necessary after metal has been repeatedly hammered.
Hammering shapes the metal and drives out impurities, but also weakens its crystalline structure, making the metal hard but brittle and easily cracked. In the case of tools where sharp edges are important such as knives , it is sometimes preferable to leave them unannealed after the final hammering, since the hardness and hence the ability to hold a sharp edge may be more important than the potential brittleness and hence the tendency to break. This process has no useful effect on pure iron or on bronze, but for iron with some carbon admixture, it produces a great increase in hardness, and it became a routine part of the production of such objects as steel swords.
Fully molten metal can be cast, that is, poured into a mold, so long as the mold has the structural integrity to withstand the heat. Since iron did not fully melt at the temperatures ancient metalworkers were able to produce, iron was normally worked by other methods outside of China , but lead, copper, and bronze were usually cast, and molds have been found from metalworking cultures around the world.
The difference in melting temperatures made iron a possible material from which to make a mold from which to produce tools made of other metals. Although such a mold would be difficult to produce, it could be used for a long time.
A specialized method of metal casting, used in the production of particularly complicated objects, is called the lost wax technique. This page is based on a wide range of sources, many of them long forgotten, and on advice from several friends and colleagues.
With the exception of the Mycenaean mask, all pictures were taken by me. Among the most useful books have been:. Go to site main page , student resources page. Copper Nugget, 2, kilos 5, pounds , found during mining operations in the Wrangell Mountains, about miles east of Anchorage. It is extraordinarily rare to find a nugget of copper this large or this pure. Museum of the North, Fairbanks.
As it comes from the mine, copper, like other mined metals, is quite impure. Private Collection. Cross section of a piece of copper ore, showing high admixture of other material.
Because of its high copper content, bronze, normally reddish in color, gradually develops a blue-green patina as the surface interacts with oxygen and other elements in the air. The unstable patina can be often be rubbed or eroded off and may therefore be uneven, as shown in this XXth-Century Chinese Bronze Figure Private Collection. Bronze is favored for public statuary, but is not indestructable.
The oxygenated copper patina not only turns green, but can be carried by rainwater runoff and even stain a stone base. XIXth-century iron cooking pot with iron stand, from Wales. Virtually identical items were common throughout northern Europe and North America. Museum of Welsh Life, Cardiff. This lidded baptismal font, dating from , was cast in soft lead. Lead was used for baptismal fonts in Britain starting in the s.
The use of lead in ceramic glazes can be dangerous, especially when the firing temperature is low or the glaze extends to the mouth of a vessel. Early XXth-century Mexican pottery, like this piece, acquired an unsavory reputation among tourists and Mexicans alike despite its attractiveness.
This famous gold mask from Mycenae is an example of the use of thin gold sheets designed to get maximum surface glitter with a minimum of material.
Mycenae, Greece. Gold processed into flat flakes and placed between sheets of shiny, non-absorbant paper to be pounded flatter. Central Myanmar.
An artisan repeatedly hammers a gold sheet, protected by non-absorbant paper and fixed in a frame, until it reaches an almost powder-like thinness for use as gold leaf. Wooden book cover for the Diamond Stura, coated with gold leaf.
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