COPPER – 2 Copper Compounds

COPPER – 2 Copper Compounds

Post 479  by Gautam Shah

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Once distinctive properties of the pure copper nodules were known, no efforts were spared to reestablish the same results. The intention was to derive a copper material easily and locally, similar to the quality of a pure copper nodule. These search resulted in discovery of many copper-containing substances. The substances were realized while processing the raw materials and finishing copper products. It helped realize many ‘copper like’ materials, but with different properties. It was found that copper became more flexible and easy to work with when heated before hammering, a process of annealing. For example, it was known that beating or forging a copper made it little brittle, but stronger for tool making. It was known that some materials could be heated to very high temperatures, in restricted air or closed environment to extract copper metal, a process of ore smelting.

Copper figure of a bull from the Temple of Ninhursag, Tell al-‘Ubaid, southern Iraq, around 2600 BC. app 600 mm

Egyptians used copper minerals like malachite and azurite for green and blue colouring the murals and also for lip colouring make-up or body colour. Copper Sulphate was used as a mordant in the dyeing to improve colour fastness. It was also used as a topical application for skin deceases and as biocide additive in mural colours. Copper compounds like cupric oxide were used in the ceramics for achieving blue, green or red tints in glasses, glazes and enamels. Chalcopyrite a mixture of pyrite and copper sulfide, is the most common copper ore, and it has been used to extract copper compounds besides the copper metal. Mineral chalcocite, a cuprous sulfide, was used as black powder.

Chalcocite

Chalcanthite-cured

Hathor, Egyptian goddess of the sky, music, dance and art, was also the patron of Sinai, the copper sourcing region for the Egyptians. She was often referred to as Lady of Malachite (the copper mineral). Copper is comparatively environment friendly material. But, historically copper ores were with natural Arsenic. The presence arsenic in copper made it a castable metal and strong enough for weapons and sharp edged tools. Osiris, an Egyptian god, often called the Great Green, is portrayed with green skin. Green malachite was a symbol of joy and the land of the blessed dead was described as the ‘field of malachite.’

Green coloured Osiris tomb of Nefertiti

The smelting process for arsenic containing copper produced poisonous fumes. Tin-bronze was a better choice as it was easier to add tin then control the amount of arsenic. But tin was comparatively rare material. Arsenic copper processing was at peak during Roman times, and its traces have been found in ice layers of Arctic regions.

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COPPER -1

Post 477 –by Gautam Shah

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Pure copper nodule 40 mm across

Copper resources of the world are estimated at nearly 5.8 trillion pounds. Of these only about 0.7 trillion pounds have been mined to date. The recycling and recovery rates of copper are so high that of nearly all of the copper mined throughout history, is still in circulation today. This means nearly 80 % of all copper ever mined is still in use today.

Malachite, Zaire> Uploaded by JJ Harrison

Copper was discovered by prehistoric man, in search of shiny stones that when beaten did not break down but rather flattened out. This was sensational discovery leading to search of shiny nodules across lands. Pure Gold and Copper nodules were forged into items of adornments and tools. It was known that several nodules of such pure metals could be forged to form a larger piece. Such nodule findings were rare. But two forms of copper carbonates greenish malachite and bluish azurite were easy to identify and collect from the grounds. Malachite was also used as a gemstone. Similarly many other bright minerals were identified.

Neoclassical vase in malachite in the Hermitage Museum, St Petersburg Uploaded by Dezidor

Azurite 80 x 60 mm Azuritechessy.jpg Uploaded by Archaeodontosaurus

Copper was known around 10000 BC or even earlier. Earliest copper object, a pendant dating 8700 BC, was found Iraq. Copper, in natural nodules form, remained a prized material for a while, but soon became a metal of utility. Unalloyed copper is soft for tools and weapons, but fairly suitable for shaping of utensils. Mesopotamia and Egypt exploited copper for creating tools used in farming, wood working, cooking, etc. These were hoes, adzes, saws, combs , pots, dishes, chisels, harpoons, cloak-pins etc. By 6000 BC it was realized that, although copper was not amenable to casting, it could be worked by hammering, chasing, engraving, and cold-rolling. Sumerians used copper sheets to form sculptures over wooden forms and fastened on walls with copper nails or wires set in bitumen.

Imdugud (also Zu or Anzu), the lion-headed eagle; Sumerian metalwork (sheets of copper), Temple of Ninhursag at Tell al-‘Ubaid; ca. 2500 BC

The Roman supply of copper almost entirely came from Cyprus, and so was known as metal of Cyprus, shortened to cyprium, later corrupted to cuprum. Copper is found at many locations as a primary mineral in basaltic lavas and also as reduced form of copper compounds. It occurs in combination with many minerals, such as chalcocite, chalcopyrite, bornite, cuprite, malachite, and azurite. It is an extremely ductile and malleable metal with high tensile strength. It is an excellent conductor of heat and electric. It is a very noble metal and by acting as a cathode can corrode other contagious metals except stainless steel. It is resistant to most acids and sea water.

Bronze decoration

A Copper alloy with tin is known as bronze. Bronze is a stronger alloy, and harder than both the pure metals. Bronze can be cast. A copper with zinc is called Brass. It was also known that by hammering the copper became hardened, ideal for creation hard edged tools. Copper and its alloys, bronze and brass, mark the first science revolution of man. However, relative scarcity of tin in many regions of the world did not allow use Bronze equally everywhere. Tin-based bronzes were preferred due to the hazard of arsenic poisoning from fumes produced by the oxidation of arsenic-containing minerals. Copper-arsenic alloys, of superior properties to copper in both cast and wrought form, were produced in many regions. Arsenic contents varied from 1 to 7 percent, with up to 3 percent tin. In many civilizations the production of pure copper, arsenical copper, and tin bronze continued together for some time.

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PATINA

Post 358 – by Gautam Shah

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India_statue_of_nataraja

Patina is a thin crust like surface layer forming on Bronze. Similar surface layers formed on other metals, stone, pottery, wood, etc. are also called Patina. Metal patina is a coating formed due to environmental exposure consisting of oxides, carbonates, sulfides, or sulfates. Patinas are formed by degradation of the surface mass and so etch or reduce its thickness. Some patinas, however, curtail further degradation of the surface and so are encouraged. Patinas are visually appealing and so desired.

Patinated and ormolu Empire timepiece representing Mars and Venus, an allegory of the wedding of Napoleon I and Archduchess Marie Louise of Austria in 1810.

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Metal artifacts exposed to different environments such air, sea-water, soils acquire patina. Similar effects can be achieved by designed exposure and by treating with various chemicals. Patinas are commonly green, but may vary in colour such as of red, brown, black, blue, or gray colours. Its surface may be smooth, glossy, or crusty. Patina also refers to accumulated changes on surface texture and colour, due to long term use of an object like coins or items of wood furniture.

Bronze_head_(Glyptothek_Munich_457)_with_and_without_patina_Bunte_Götter_exhibition

Desert patina or Varnish is a thin, dark red to black mineral coating (of iron and manganese oxides and silica) seen on exposed pebbles and rocks in desert terrains. This is deposition of moisture dissolved minerals drawn to the surface by capillary action of evaporation. Wind abrasion removes the softer salts, and polishes the surface to a glossy finish. In geology and geomorphology, the stone patina also refers to a casehardened layer, called cortex, or corticated layer on the surface of Flint tools or a chert nodule.

Desert Varnish stones

PATINA has probable origin from a Latin word for shallow dish, or patere’, =to lie open. By extension, the word is applied to the discoloured or incrusted surface of marble, flint, etc. The chemical process, by which patina forms, is called patination, and an artefact coated by patina is said to be patinated. Newly made objects are deliberately patinated to simulate the antiquity. The process is often called distressing.

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Firearms nominally carry Parkerizing, a bluing finish, (bonderizing, phosphating or phosphatizing) a conversion coating treatment for corrosion and wear resistance to a steel surface. These objects develop patina after the bluing finish gets worn. Firearms with such patina finish are highly valuable antiques.

Statue of Liberty NY USA -Patina

Patinas are created over frying-cooking vessels such as Kadhai and Tava (frying pan and Roti baking pan, India), Woks for Chinese preparations, and other metal baking dishes, by seasoning them with oils and salts, when used for the first time. The patina prevents rusting and food sticking to the vessels. To protect the patina, such vessels are scrubbed lightly, and washed gently with cold water.

Chinese Wok

Verdigris is the natural patina formed over copper, brass or bronze, when exposed to the air or seawater, over a period of time. It is usually a basic copper carbonate, but near the sea could be a basic copper chloride. The name verdigris comes from the Middle English vertegrez, from the old French verte grez, an alteration of vert-de-Grèce =green of Greece or vert-de-gris =green of grey.

464px-WLA_cma_Young_Woman_Nursing_Her_Child_bronze_with_brown_patina

Patina over copper alloys, such as bronze, due to the chlorides leads to green, while sulfur compounds are brown. The basic palette for patinas on copper alloys is blue-black due to ammonium sulfide, brown-black with liver of sulfur, blue-green for cupric nitrate, and yellow-brown due to ferric nitrate. For new artefacts accelerated patination carried out by applying chemicals with heat. Colours range from matte sandstone yellow to deep blues, greens, whites, reds and various blacks. Some patina colours are achieved by the mix of pigments and chemicals. The surface is enhanced by waxing, oiling, or other types of lacquers or clear-coats. French sculptor Auguste Rodin used to instruct assistants to urinate over bronzes stored or buried in the yard. A temporary-washable patina is produced on copper by vinegar (acetic acid).

Auguste Rodin Balzac Bust 1892

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In architecture, metals, like copper, bronze, etc. have been used for a very long time, for wall cladding, door panelling, ceiling tiles, and roof covering. Copper provides excellent corrosion resistance. Copper surfaces form tough oxide-sulfate patina coating that protects underlying copper mass and resists further corrosion. Copper corrosion products are less toxic. Copper sheets have been used in many building to cover rounded domes, and articulated roof surfaces. Architectural copper is, though susceptible to oxidizing acids, heavy-metal salts, alkali, sulfur and nitrogen oxides, ammonia, sulfur and ammonium compounds. Brass, an alloy of copper and zinc, has good resistance to atmospheric corrosion, alkali, and organic acids.

Kresge Auditorium MIT

One of the most common surface degradation products is rust on steels Rust is flaky and friable, and it provides no protection to the underlying iron, unlike the formation of patina on copper or bronze surfaces. Rust is permeable to air and water, therefore the interior metallic iron beneath a rust layer continues to corrode. Rust prevention thus requires coatings that preclude rust formation.

Copper Roof Dresden