History of gold working 3000 BCE	Gold	http://info.goldavenue.com/Info_site/in_arts/in_civ/in_civ_overview.html
Bronze 3000 BCE	UNC	[Link not active Aug 07] http://www.unc.edu/courses/rometech/public/content/arts_and_crafts/Sara_Malone/BRONZE_2.html
Stone, Bronze, Iron	SBI	http://www.naciente.com/essay88.htm
Late Bronze, early Iron images		http://www.hp.uab.edu/image_archive/uj/ujd.html
Copper	UNR	http://www.unr.edu/sb204/geology/copper2.html
Copper metallurgy	CC	http://www.citycollegiate.com/dblock4.htm

Metals and Metallurgy

The main source of material in this section has been Chemistry The Central Science, 8^th Edition, by Brown, LeMay, and Bursten,, BLB. See also the various web links. Also the Encyclopedia of World Art, Volume IX, Metalwork (pages 790-798 and on to 827) (Ref. N 31.E4833), EWA, was used.

The early history of metalworking was entirely of a functional nature at first, producing instruments, utensils, and weapons. Metalworking often accompanied working with wood, bones, stones, and early forms of pottery.	EWA 790
Only later was metalworking used for artistic purposes, first ornamental personal objects, and later larger decorative and figural pieces (as in gates).	EWA 790
One major use of metalworking was in making coins.
Several sources divide early history into three time periods based on the compositions of tools used: Stone Age, Bronze Age, and Iron Age	BLB 897
In about 8000 BCE, copper was found in its elemental state and beaten into ornaments and soft weapons. It was hammered into shapes but became brittle and needed to be reheated to be further worked on. Later (about 5000 BCE) when higher temperatures could be achieved, copper was melted and poured into molds to make tools and weapons. The melting point of Cu is 1084 °C. (1983 °F.). See the figures in UNC for the types of kilns that were being used to produce ceramics. Also extra air had to be added to increase the temperature. Copper was the main metal of earliest metal history because of its abundance and extensive distribution. Early copper was found near the surface, but by the 2^nd millennium BCE, true mines were used. True metallurgy began with the discovery of copper smelting. But open fires are not good because of the presence of air/oxygen. Again the heating techniques developed by ceramicists were used in smelting. The pottery kilns are very similar to the early copper smelting kilns. Heat was sufficient. So placement of fuel and ore were important.	EWA 791	SBI UNC * UNR (lots of interesting info)
In about 5000 BCE, gold was first discovered in its elemental state and beaten into ornamental objects In nature, gold is sometimes found alloyed with silver, in a substance called electrum. The oldest gold objects were made from this electrum.	BLB Ch4	SBI Gold
In about 3500 BCE, someone found that some tin could be mixed with copper to produce bronze, a harder form of metal than pure copper. Lead is also sometimes included. Only with bronze’s excellent casting qualities could larger statues be produced. Though copper was wide spread, tin was not. Centers of bronze production were located near sources of both ores to cut down on transportation. By about 1500 BCE bronze was the predominant metal in Europe and parts of Asia.	EWA 791, 793	SBI UNC *
In about 900 BCE, someone found that if you mixed zinc with copper, you could form another alloy, brass. An advantage to brass over bronze was its gold coloring.
In about 1500 BCE, iron metal was produced from ores that were present in many places. Higher temperatures were needed and a way to remove the oxygen from the iron ores. Charcoal was used to remove the oxygen. Even then the product needed to be worked (reheating, pounding) to produce a usable metal.		SBI UNC *
Early metallurgy took place in Iran, Mesopotamia, and Egypt and was well in place in the 4^th millennium BCE. Metallurgy practice spread from there.	EWA 792
Early working for artistic purposes of copper, gold, and silver used sheets of metal. To form a shallow bowl, the metal sheet was beaten down into a the depression of a wooden mold. ‘Raising’ was another method –which is not clear to me. Repoussé was applied to sheets of metal by hammering from the front or back to give a raised pattern (relief). Later plates were attached to each other with rivets. Punching and engraving were used for decoration. Soldering and fusing were used for welding pieces together. Turning, spinning, and inlay work were started by specialist artists.	EWA 793, 794
Ores
Most metals occur in ores. BLB defines an ore as ‘a source of a desired element or mineral, usually accompanied by large quantities of other materials such as sand and clay.’ A mineral is a ‘solid, inorganic substance which is naturally occurring.’ Many metal ores are only found in limited locations, leading to international politics. Also, mining often distorts the local landscape. Most minerals are oxides and sulfides, sometimes carbonates and hydroxides. Silicates are abundant but hard to concentrate.	BLB 898, G-10
Metallurgy is the science dealing with separating metals from the ores and then preparing the metals for final use. BLB suggests five steps: 1) mining 2) concentrating the ore and prepare the ore for treatment 3) reducing the ore to the free metal 4) refining or purifying the metal 5) mixing the metal with other metals to change the properties, the result being an alloy.	BLB 899
Step 2) uses various means, always capitalizing on any properties that are different between the metal of interest and the rest of the ore, called the gangue. Gold miners used a pan to wash away the impurities from the more dense gold. A magnetic metal can be removed from the gangue by using magnets.
Step 3) is probably the hardest part, and in any case the most interesting part as far as chemistry is concerned. The three main methods of reduction are a) by heat, pyrometallurgy; b) using reactions of water solutions, hydrometallurgy; c) using electrolysis, electrometallurgy.	BLB 900 ff
a. pyrometallurgy, pyro meaning high temperature.
i. *calcination: the process of heating an ore to decompose it and form a volatile product, i.e., a gas, typically carbon dioxide, CO₂, or water. Carbonates are calcined to produce carbon dioxide, viz: CaCO₃ is heated (usually represented by an arrow with a triangle (heat) over it.) to produce CaO (s) and CO₂ (g). CaCO₃ (s) -> CaO (s) and CO₂ (g). Note that the ending –ate* means the anion contains oxygen, e.g., carbonate, CO₃^2-; sulfate, SO₄^2-; and nitrate, NO₃^- Temperatures range usually from 400 to 500 °C. 1000 °C is needed for calcium carbonate. Metal hydrates often lose their water of hydration in the range 100 to 300 °C. For example, blue CuSO₄^.5H₂0 is converted to anyhydrous CuSO₄with a low heat of about 150 °C.	BLB 900
ii. *roasting*: heating again, but this time there is a reaction between the ore and the atmosphere (gases present) in the furnace. If oxygen is present (an oxidizing atmosphere!), the ore will be oxidized. How does that help? If the ore is a sulfide, then the S is converted to SO₂ gas, and the gas rises into the atmosphere (which can be bad! Think of Copper Hill, TN, and the acid rain problems, viz: SO₂ (g) + H₂O -> H₂SO₃.) The metal winds up as an oxide, which must still be dealt with somehow. Ex: 2 CuS (s) + 3 O₂ (g) -> 2 CuO (s) + 2 SO₂ (g) You should identify which substances are oxidized and which reduced in these and other reactions. Less active metals, such as Hg, can be roasted to the ‘free’ metal: HgS (s) + O₂ (g) -> Hg (l) + SO₂ (g) If a reducing atmosphere is present, some metal ores can be changed to the free metal. What is a good, and common, reducing atmosphere gas? CO, carbon monoxide, which can be produced by burning wood and particularly charcoal, in a limited amount of oxygen. (If there is excess oxygen, the C becomes carbon dioxide, CO₂.) Ex: PbO (s) + CO (g) -> Pb (l) + CO₂ (g) The more active metals (the ones hard to reduce) can’t be produced by roasting.	BLB 900
iii. *smelting*: heating and chemical reactions yet again, this time with the goal of melting the ore to produce materials which separate into two or more layers. Roasting often occurs as a stage in the process and in the same furnace. Two important layers are molten metal and slag. The molten metal may or may not be a pure metal. The slag is a molten silicate material which is usually less dense than the molten metal and thus floats on the metal. The slag and metal can be drawn off separately from the furnace.	BLB 900
Pyrometallurgy of iron. There are many iron ores, but two of the most used are hematite, Fe₂O₃, and magnetite, Fe₃O₄ (really a 1:1 mixture of FeO and Fe₂O₃). Iron ore, limestone (CaCO₃), and coke (coal that has been heated in the absence of air to rid of volatile components and produce a product that is 85-90% C) are added at the top of a blast furnace. The coke is the fuel that produces heat as it burns in the lower part of the blast furnace. The coke also produces the reducing gases CO and H₂. Hot air comes in from the bottom. A limited supply of oxygen reacts with the coke: 2 C (s) + O₂ (g) -> 2 CO (g) Water vapor can react with the coke: C(s) + H₂O (g) -> CO (g) + H₂ (g) You should continue to identify which substances are oxidized and which reduced in these and other reactions. The limestone is calcined (see above) in the upper part of the furnace. And here also the iron oxides are reduced by the rising CO and H₂ gases. Viz: Fe₃O₄+ 4 CO (g) -> 3 Fe (s) + 4 CO₂ (g) and Fe₃O₄+ 4 H₂ (g) -> 3 Fe (s) + 4 H₂O (g) In the lower, hotter parts of the furnace other elements that are present in the ore can be reduced. Here C, rather than CO, is the major reducing agent. The CaO from the calcinations process reacts with silica present in the ore to form slag. The slag acts to protect the molten iron from being reoxidized. From time to time, molten iron is removed. Slag is also removed. Most of the iron produced is further treated to remove remaining impurities. Alloying elements are then added to produce steel.	BLB 901
b. hydrometallurgy: The pyrometallurgy methods require a lot of energy and usually produce gases that cause pollution in the atmosphere. In hydrometallurgy, ores are treated with aqueous solutions to extract the metals. In the process, the water may become polluted. So, trading one kind of pollution for another!	BLB 903
*leaching* is the most important hydrometallurgical process. The goal is to dissolve the compound containing the metal selectively, i.e., just dissolve what is wanted. Sometimes water alone can be used; more commonly acid, base, or a salt is added. Low-grade gold ores can be treated with sodium cyanide, NaCN, oxygen and water, viz: 4 Au (s) + 8 CN^- (aq) + O₂ (g) + 2 H₂O (l) -> 4 Au(CN)^2- (aq) + 4 OH^- (aq) This reaction gets the gold into solution in what is called a complex ion, Au(CN)₂^- . To produce the gold metal, Zn is added, viz: 2 Au(CN)^2- + Zn(s) -> Zn(CN)₄^2- + 2 Au (s)	BLB 904
Al is the metal in highest concentration on the earth’s surface. And next to iron is the most commercially used metal. Bauxite is the most useful Al ore, and has the general formula Al₂O₃^.xH2O, where the value of x varies depending on the source of the ore. Common impurities are hematite and silica, SiO₂. Al is eventually produced by electrochemical reduction of alumina, Al₂O₃ . But first the hematite and silica must be removed. The Bayer process is a hydrometallurgical process. In a concentrated solution of sodium hydroxide, NaOH, at moderate temperatures (150-230 ° C), and at a relative high pressure to prevent boiling is added to the bauxite. A complex ion of Al(OH)₄^- is formed, which can be separated from the impurities.	BLB 904
c. electrometallurgy: the process to obtain and/or purify metals by the use of electrolysis (using high voltage to make a nonspontaneous oxidation-reduction reaction take place). This kind of process is necessary to win the more active metals from their compounds, e.g., Na, Mg, Al.	BLB 905
Copper is often purified using electrorefining. Impure copper is oxidized at the anodes of a cell. Thin pieces of pure copper are used as the cathodes, and copper ions are reduced.	BLB 907