<<<Back to the list

Pipe metal

Metal used for the making of organ pipes. It is made from a combination of tin, lead or a combination of these 2 metals. On occasion other trace elements are added, such as antimony or bismuth. Generally the higher the tin content of the pipe, the brighter the tone, and the higher the lead content the more mellow the tone. Pipe metal is also used in the making of metal tubing for transmitting wind).

The metals used in organ pipes

     Lead was one of the first metals known to man. Probably the oldest lead artifact is a figure made about 3000 BC. All civilizations, beginning with the ancient Egyptians, Assyrians, and Babylonians, have used lead for many ornamental and structural purposes. Many magnificent buildings erected in the 15th and 16th centuries still stand under their original lead roofs.

Lead-Base Alloys

     Because lead is very soft and ductile, it is normally used commercially as lead alloys. Antimony, tin, arsenic, and calcium are the most common alloying elements. Antimony generally is used to give greater hardness and strength, as in storage battery grids, sheet, pipe, and castings. Antimony contents of lead-antimony alloys can range from 0.5 to 25%, but they are usually 2 to 5%.

     Lead-calcium alloys have replaced lead-antimony alloys in a number of applications, in particular, storage battery grids and casting applications. These alloys contain 0.03 to 0.15% Ca. More recently, aluminum has been added to calcium-lead and calcium-tin-lead alloys as a stabilizer for calcium. Adding tin to lead or lead alloys increases hardness and strength, but lead-tin alloys are more commonly used for their good melting, casting, and wetting properties, as in type metals and solders. Tin gives the alloy the ability to wet and bond with metals such as steel and copper; unalloyed lead has poor wetting characteristics. Tin combined with lead and bismuth or cadmium forms the principal ingredient of many low-melting alloys.

     Arsenical lead (UNS L50310) is used for cable sheathing. Arsenic is often used to harden lead-antimony alloys and is essential to the production of round dropped shot.

Properties of Lead

     The properties of lead that make it useful in a wide variety of applications are density, malleability, lubricity, flexibility, electrical conductivity, and coefficient of thermal expansion, all of which are quite high; and elastic modulus, elastic limit, strength, hardness, and melting point, all of which are quite low. Lead also has good resistance to corrosion under a wide variety of conditions. Lead is easily alloyed with many other metals and casts with little difficulty.
The high density of lead (11.35 g/cm3, at room temperature) makes it very effective in shielding against x-rays and gamma radiation. The combination of high density, high limpness (low stiffness), and high damping capacity makes lead an excellent material for deadening sound and for isolating equipment and structures from mechanical vibrations.

     Malleability, softness, and lubricity are three related properties that account for the extensive use of lead in many applications.

     The low tensile strength and low creep strength of lead must always be considered when designing lead components. The principal limitation on the use of lead as a structural material is not its low tensile strength but its susceptibility to creep. Lead continuously deforms at low stresses and this deformation ultimately results in failure at stresses far below the ultimate tensile strength. The low strength of lead does not necessarily preclude its use. Lead products can be designed to be self-supporting, or inserts or supports of other materials can be provided. Alloying with other metals, notably calcium or antimony, is a common method of strengthening lead for many applications. In general, consideration should always be given to supporting lead structures by lead-covered steel straps. When lead is used as a lining in a structure made of a stronger material, the lining can be supported by bonding it to the structure. With the development of improved bonding and adhesive techniques, composites of lead with other materials can be made. Composites have improved strength yet also retain the desirable properties of lead.

Tin, Lead, and Lead Alloy Corrosion

     Articles of tin are seldom encountered in archaeological sites. This metal is found more often in various alloys, particularly in combination with copper for bronze and/or tin pewter. Tin seldom survives in archaeological sites because of the transformation of tin to a mix of stannous and stannic oxide by direct intercrystalline oxidation (SnO and SnO2) or to a loose powdery gray tin, commonly referred to as 'tin pest,' by allotropic modification The alteration compounds of tin in a marine environment have not been adequately studied; it is known, however, that sodium chloride stimulates the corrosion of tin. Ingots of tin that were completely oxidized to tin oxide were recovered from a Bronze Age shipwreck off the coast of. Although not often mentioned in literature, tin sulfide can also be expected to be found where sulfate-reducing bacteria are active in anaerobic environments.

     Lead is commonly found in shipwrecks; it was used on ships for weights, cannonballs, sheeting, and stripping. Lead is a stable metal in neutral or alkaline solutions that are free from oxidizing agents, especially if carbonates are present in the water. Basic lead carbonate (2PbCO3 0 Pb[OH]2) and lead oxides (PbO and Pb O2) are formed under most archaeological conditions where there is prolonged atmospheric exposure. The gray lead carbonate and lead oxide generally form a protective layer on the artifact that prevents further oxidation. Both these corrosion compounds are found on lead from a marine environment, but lead chloride (PbCl2), and especially lead sulfide (PbS) and lead sulfate (PbSO4), are also common.

     Few occurrences of lead sulfide have been reported on archaeological objects, but primary lead corrosion product in anaerobic marine environments is lead sulfide, while lead sulfate is commonly found on objects recovered from aerobic marine environments. It is not unusual in shipwreck excavations to find the remains of lead straps that have been completely converted to a black slush. The bulk of this corrosion is most likely lead sulfide which results from the action of sulphate-reducing bacteria. Some intermediate forms of lead oxides (PbO and PbO2) may be formed, and oxysulfides are also present. Lead often exhibits extensive corrosion attack when it is in contact with wood. Lead strips that were nailed onto a ship's keel have been observed in a state of severe deterioration. The oxygen-consuming, decaying wood and the marine encrustation that forms over the lead apparently creates the anaerobic conditions conducive for the metabolism of the sulfate-reducing bacteria; in addition, the decaying wood provides nourishment for the bacteria.

     Lead alloys, such as old pewter, which is an alloy of tin and lead, oxidize to the same compounds as the two parent metals. The condition of different pewter pieces varies widely both between and within archaeological sites, primarily because of different local conditions and varying percentages of tin to lead in each individual object. In general, leaded pewter always survives in better condition in marine environments than does lead-free pewter; this is most likely due to the formation of lead sulfate (PbSO4) that protects the surface of the artifact. Lead-free pewter suffers extensive corrosive attack in aerobic sea water and is often completely mineralized as stannic oxide (SnO2) and lead sulfide (PbS), and various very brittle, mineralized antimony and tin (SbSn) compounds are formed. In contrast, in anaerobic environments, both leaded and lead-free pewter survive in good condition through the protective formation of lead and tin sulfide films. In fact, the only corrosion present on pewter recovered from anaerobic marine environments may be a thin sulfide film on the surface of well-preserved metal. Various combinations of lead carbonate, lead oxide, lead sulfide, lead chloride, and tin oxide are possible. Pewter objects often have wart-like blisters on the surface of the metal, which possibly result from localized contaminations of salts. These should not be removed, for under most of them there are either holes or pits in the metal.

CONSERVATION OF LEAD, TIN, AND PEWTER

     Once recovered from the sea, the corrosion products of objects of lead, tin and their alloy, pewter, are stable. The corrosion products may be unsightly or even disfiguring, but they do not take part in chemical reactions that attack the remaining metal. The objects should be cleaned only for aesthetic reasons and to reveal surface details under the corrosion layers. Old pewter, an alloy of lead and tin, must be treated as tin, which is the more anodic and chemically sensitive metal. Therefore, no acids, or sodium hydroxide should be used, unless, in the case of electrolysis, the metal is given cathodic protection.

CHEMICAL TREATMENT OF LEAD

     Because of the ease of treatment and the availability of the chemicals, the most widely used conservation treatment for lead from any archaeological environment is the acid treatment. The lead is immersed in 10 percent hydrochloric acid, which will remove any adhering marine encrustation, along with lead carbonates, lead monoxide, lead sulfide, calcium carbonate, and ferric oxide. This treatment is good for lightly corroded specimens, and it gives lead surfaces a pleasing appearance. The surface detail that is preserved by this treatment varies with the degree of corrosion when recovered. For more diagnostic lead artifacts, Another method has been superseded by electrolytic reduction, which has the ability to convert mineral products back to a metallic state. For the general cleaning of lead without a lot of hands-on labor, however, This method remains an acceptable and much-used technique, provided that the object is thoroughly rinsed after treatment in order to remove all remaining hydrochloric acid residue. This will prevent contamination of any chloride-sensitive material with which the treated lead may be stored.

     If lead dioxide is present, it can be removed by soaking the object in 10 percent ammonium acetate. The ammonium acetate will also act as a buffer to protect the lead from the action of any hydrochloric acid that may remain. If treated with ammonium acetate, lead should be left in the solution only as long as necessary, as the solution can etch the metal. For most lead objects, however, the ammonium acetate step is not required.

     If the objective is to completely remove all of the lead corrosion products from a lead object, a 5 percent solution of ethylenediaminetetraacacetic acid (EDTA) disodium salt is most effective. After complete immersion in the EDTA solution for two to three hours (up to 24 hours for large objects), the object is rinsed in tap water.

     After treating lead, the conservator still has the option to use electrolytic to reduce any corrosion layer that are still in place back to a metallic state.

GALVANIC CLEANING OF LEAD

     Any solid object of tin can be cleaned galvanically or by electrolytic reduction in the same way as described for iron and the other metals. Normally, in galvanic cleaning, the vat with the electrolyte, anodic metal, and specimen is heated to speed the reaction; however, since tin is an allotropic metal that is slightly soluble in sodium hydroxide, heating should be avoided and the treatment time kept to a minimum. Tin coins respond well to cold electrochemical reduction, using zinc, aluminum, or magnesium powder in caustic soda. Magnesium is often substituted for zinc, since zinc sometimes discolors the tin. However, if electrolytic reduction equipment is available, there is little reason to use galvanic cleaning for any object of lead, tin, or their alloys.

     The only conservation alternative for badly oxidized tin objects is to consolidate them in microcrystalline wax or embed them in a plastic material. Slow, extended diffusion of chlorides in an alkaline solution is not an option due to the solvent action of the solution on tin objects.

ELECTROLYTIC REDUCTION CLEANING

     The ability to control the speed of the electrolytic reaction through current controls makes electrolytic reduction especially useful for lead coins and medals or, indeed, any specimen where surface detail is important or reduction and/or consolidation of the corrosive layers is the objective. Two electrolytic reduction techniques, normal reduction and consolidative reduction are used for treating lead.

Normal Reduction

     Lead artifacts with substantial metal remaining can be cleaned by the normal electrolytic reduction process using 5 percent sodium hydroxide, anodes of mild steel or stainless steel, and a current density of 2-5 amps/dm2. Very satisfactory results are achieved by this technique. However, since lead is susceptible to solvent action by the electrolyte, when it is not cathodically protected, the current must be flowing before putting the specimen in the electrolytic tank and must not be cut off while the specimen is immersed in the tank. A good electrical contact, as indicated by evolution of hydrogen from the object, must be made with the lead, and the contact should be sufficiently supported to ensure that the electrical contact is maintained.

     Since lead, tin, and pewter are susceptible to attack by strong alkalies, a sodium carbonate electrolyte is safer for use in electrolysis than a sodium hydroxide electrolyte. If the electricity were to go off during electrolysis while the lead or tin object or alloy was immersed in NaOH, the object would be attacked by the alkaline solution. If sodium carbonate was being used as the electrolyte, however, a passivating film of carbonate would form on the object, and the alkaline attack would stop. The attack on tin and tin alloys by sodium hydroxide solution is particularly aggressive. Since sodium carbonate does a reasonably good job on artifacts made of these metals, the use of sodium hydroxide electrolytes should be reserved for consolidative reduction on special artifacts where there is some reason to attempt to achieve the absolute maximum reduction of corrosion products back to metal. For example, when there are inscriptions or marks that are preserved in the corrosion layer of an object, sodium hydroxide should be used as the electrolyte.

Consolidative Reduction

     The technique was developed to consolidate the inscriptions contained in a fragile corrosion layer of basic lead carbonate on a group of lead seals. The removal of the corrosion layer would have obliterated the inscription. Consolidative reduction converts the basic lead carbonate and other lead corrosion products to a compact mass of lead. The object is tightly compressed between two polyurethane foam pads in order to support and put pressure on the corrosion layers while they are cathodically reduced at a current density of 100 to 200 milliamps/dm2.

     In consolidative reduction, which employs very low current densities, mild steel anodes cannot be used because the current flow is so low that there is no way to keep the anodes passivated against anodic dissolution; therefore, stainless steel anodes and a 5 percent sodium hydroxide electrolyte are recommended. The procedure using a 10 percent solution of sulfuric acid with a lead anode, is not common because of the difficulties of handling sulfuric acid and the deposition of lead from the anodes onto the artifacts being treated. In addition, more recent research has shown that the most thorough reduction is achieved when NaOH is used as the electrolyte.

      It is suggested using a partially rectified alternating current source, which provides a 'bumping' effect, for better results. As discussed in the section on silver, however, the use of an asymmetrical alternate current is not widely used since low current density electrolysis using straight direct current effectively reduces lead corrosion products back to metallic lead, especially when sodium hydroxide is used as the electrolyte. The use of an asymmetrical alternate current does not appear to increase the degree of reduction. The most important thing for the conservator to keep in mind during any electrolytic cleaning process is the importance of maintaining a constant flow of electrons to the lead or tin metal that is being treated to ensure cathodic protection.

Rinsing Procedure Following Electrolytic Reduction

     Sodium hydroxide electrolyte residues cannot be removed completely from lead through simple water rinsing; a more complex procedure must by followed. The object should be submerged in a dilute solution of sulfuric acid (4 drops of concentrated (15-18%) H2SO4 per liter of tap water) with a pH of 3 to 3.5 neutralizes the alkalinity of the electrolyte and forms a protective coat of lead sulfate on the surface of the object. The artifact is then taken through a succession of H2SO4 baths until the pH ceases to rise due to the diffusion of alkali from the lead. After removal from the sulfuric acid bath, the residual acidity present on the surface of the lead is removed through immersion of the object in successive baths of cold distilled water with a pH of about 6, until the pH of the water does not drop.

SEALANT

     Following the rinsing, the reduced object is dried with hot air or dehydrated in a water-miscible solvent. The fragile reduced metal is then strengthened and protected from atmospheric corrosion by submersion in molten microcrystalline wax.

STORAGE

     Lead is particularly susceptible to organic acids, such as acetic acid, humic acid, and tannic acid. Lead artifacts, therefore, should not be stored in oak cabinets or drawers. If so, even small concentrations of vapors of these acids can initiate corrosion, which progresses rapidly. To be safe, lead should by stored in sealed containers or polyethylene bags.

Where does tin come from?

     Tin is obtained from the mineral cassiterite which is tin oxide SnO2. Brazil, Bolivia, China, Indonesia, Thailand and Malaysia and now Peru are significant producers. The Cornish mines were almost completely wiped out by the price collapse of 1985 with only South Crofty still working in recent years. Whilst idle and almost completely flooded negotiations continue to purchase and restart the mine.

Smelting
     Cassiterite is smelted to metal by reduction with carbon most commonly in a reverberatory furnace. Temperatures in excess of 1200C are required. The difficulty is that cassiterite is hardly ever produced entirely free from other minerals many of these are reduced to metal at the same time forming alloys with the tin. It is therfore necessary to refine the tin to make it commercially useful. Fire refining involves various procedures on the molten metal. Iron is removed by passing steam through the molten metal, arsenic and antimony are removed by additions of aluminium alloy and copper is removed with sulphur. Very impure tin can be refined by electrolysis to very high purity.

Tin and it's Alloys

     One of the most important properties of tin is the ease with which it alloys or mixes with the majority of other metals, it is this quality together with the low melting point which makes it an essential ingredient of most solders. It is not toxic and it does not corrode all that rapidly making it ideal as a protection for steel for food and drinks 'tin cans' properties which are also important in pewter. The very high boiling point allows it to be used as a smooth molten surface to make 'float' glass.

Some remarkable tin alloys

     An alloy of 80% gold 20% tin melts at around 280C this would easily allow casting into rubber molds! This alloy is used as a special solder and has a slight green colour.
An alloy of tin, bismuth, lead and cadmium in the right proportions will melt well below the boiling point of water at just 70C

     Pewter is a tin alloy which has had many compositions through the ages the only common ingredient being a high tin content, pewter exploits the beauty and ease of working of tin with additions of other metals being made mostly to strengthen it.

     Bronze is regarded as an alloy of tin and copper usually less than 12% tin although it often includes other metals to meet specific requirements. Bronze is the first tin alloy used by man but there is much debate about when and how we first deliberately mixed tin and copper as an alloy. Many early 'bronzes' don't contain much tin. Higher tin bronzes are used to cast bells. Brass does not normally contain tin being an alloy of copper and zinc

     Solder alloy compositions are numerous but the most important are still the tin lead solders which were used by the Romans. Tin melts at around 232C and lead at about 327C in the combination 63Sn 37Pb the resulting alloy melts at 183C. This composition is known as the eutectic. Solders used in electronics account for a significant proportion of tin consumption. Lead free plumbing solder is often tin with about 0.5% copper although many other compositions have been developed.

     Tin was one of the first metals known to man. Throughout ancient history, various cultures recognized the virtues of tin in coatings, alloys and compounds, and use of the metal increased with advancing technology. Today, tin is an important metal in industry even though the annual tonnage used is much smaller than those of many other metals.               

     One reason for the small tonnage is that, in most applications, only very small amounts of tin are used at a time.

Tinplate.

     The largest single application of tin is in manufacture of tin-plate (steel sheet coated with tin), which accounts for about 40% of total world tin consumption.
Since 1940, the traditional hot dip method of making tinplate has been largely replaced by electrodeposition of tin on continuous strips of rolled steel. Electrolytic tin-plate can be produced with either equal or unequal amounts of tin on the two surfaces of the steel base metal. Nominal coating thickness for equally coated tinplate range from 0.38 to 1.54 m on each surface. The thicker coating on tinplate with unequal coatings (differential tinplate) rarely exceed 2.0 m. Tinplate is produced in thickness from 0.15 to 0.60 mm.

     Over 90% of world production of tinplate is used for containers (tin cans). Tinplate cans find their most important use in packaging of food products, beer and soft drinks, but also are used for holding paint, motor oil, disinfectants, detergents and polishes. Other applications of tinplate include fabrication of signs, niters, batteries, toys, gaskets, and containers for pharmaceuticals, cosmetics, fuels, tobacco and numerous other commodities.

Electroplating

     It accounts for one of the major uses of tin and tin chemicals. Tin is used in anodes, and tin chemicals are used in formulating various electrolytes, for coating a variety of products. Tin electroplating can be performed in either acid or alkaline solutions. Sodium or potassium stan-nates form the bases of alkaline tin plating electrolytes that are very efficient and capable of producing high-quality deposits.

Hot Dip Coatings.

     Coating of steel with lead-tin alloys produces a material called tern plate. It is easily formed and easily soldered and is used as a roofing and weather sealing material and in construction of automotive gasoline tanks, signs, radiator header tanks, brackets, chassis and covers for electronic equipment and sheathing for cable and pipe.
Hot dip tin coatings are used on wire for component leads as well as food handling and processing equipment.

Unalloyed Tin.

     There are only a few applications where tin is used unalloyed with other metals. Unalloyed tin is well recognized as the most practical lining material for handling high-purity water in distillation plants because it is chemically inert to pure water and will not contaminate the water in any way.

Tin in Alloys.

     Solders account for the second largest use of tin (after tinplate). Tin is an important constituent in solders because it wets and adheres to many common base metals at temperatures considerably below their melting points. Tin is alloyed with lead to produce solders with melting points lower than those of either tin or lead. Small amounts of various metals, notably antimony and silver, are added to tin-lead solders to increase their strength. These solders can be used for joints subjected to high or even subzero service temperatures.

     Both solder compositions and applications of joining by soldering are many and varied. Commercially pure tin is used for soldering side seams of cans for special food products and aerosol sprays. The electronics and electrical industries employ solders containing 40 to 70% tin, which provide strong and reliable joints under a variety of environmental conditions. General-purpose solders (50Sn-50Pb and 40Sn-60Pb) are used for light engineering applications, plumbing and sheet metal work. Lower-tin solders (20 to 35% Sn, remainder Pb) are used in joining cable and in production of automobile radiators and heat exchangers. Low-tin solders are used in large amounts to fill crevices at seams and welds in automotive bodies, thereby providing smooth joints and contours. Solders containing about 2% tin (remainder lead) are used for can side seams to provide hermetic seals. Tin-zinc solders are used to join aluminum, while tin-antimony and tin-silver solders are employed in applications requiring joints with high creep resistance.

Alloys for Organ Pipes.

     Tin-lead alloys are used in the manufacturing of organ pipes. These materials commonly are named "spotted metal" because they develop large nucleated crystals or "spots" when solidified as strip on casting tables. The pipes that produce the diapason tones of organs generally are made of alloys with tin contents varying from
20 to 90% according to the tone required.

Pewter

     Is a tin-base white metal containing antimony and copper. Originally, pewter was defined as an alloy of tin and lead, but to avoid toxicity and dullness of finish, lead is excluded from modern pewter. These modem compositions contain 1 to 8% antimony and 0.25 to 3.0% copper.

Bearing Materials.

     Tin has a low coefficient of friction, which is the first consideration in its use as a bearing material. Tin is structurally a weak metal, and when used in bearing applications it is alloyed with copper and antimony for increased hardness, tensile strength and fatigue resistance. Normally, the quantity of lead in these alloys, called tin-base babbits, is limited to 0.35 to 0.5% to avoid formation of the tin-lead eutectic, which would significantly reduce strength properties at operating temperatures.

     Lead-base bearing alloys, called lead-base babbits, contain up to 10% tin and 12 to 18% antimony. In general, these alloys are inferior in strength to tin-base babbits, and this must be equated with their lower cost.

     Bearing alloys must maintain a balance between softness and strength. Aluminum-tin bearing alloys represent an excellent compromise between the requirements for high fatigue strength and the need for good surface properties such as softness, seizure resistance and embed ability. Aluminum-tin bearing alloys are usually employed in conjunction with hardened steel or ductile iron crankshafts and allow significantly higher loading than tin- or lead-base bearing alloys.

     Low-tin aluminum-base alloys (5 to 7% Sn) containing small amounts of strengthening elements, such as copper and nickel, are often used for connecting rods and thrust bearings in high-duty engines. Strict dimensional tolerances must be adhered to and oil contamination should be avoided. Alloys containing 20 to 40% tin, remainder aluminum, show excellent resistance to corrosion by products of oil breakdown and good embeddability, particularly in dusty environments. The higher-tin alloys have adequate strength and better surface properties, which make them useful for crosshead bearings in high-power marine diesel engines.

Battery-grid Alloys.

     Lead-calcium-tin alloys have been developed for storage-battery grids largely as replacements for antimonies lead alloys. Use of ternary lead-base alloys containing up to 1.3% tin has substantially reduced gassing, and therefore batteries whose grids are made of these alloys do not require periodic water additions during their working life. Two chief methods of grid manufacture are casting and fabrication of wrought alloys including punching, roll forging and expanded metal processes.

Copper Alloys.

     Copper-tin bronzes were some of the first alloys used by man, and these alloys continue to be used for structural and decorative purposes. True bronzes contain tin in amounts up to 10% as well as very small amounts of phosphorus. Quaternary bronzes containing 5% Sn, 5% Zn, 5% Pb, and remainder Cu are used for general-purpose castings for applications requiring reasonable strength and soundness, such as gears, pumps, and automotive fittings.

Dental alloys

     For making amalgams contain silver, tin, mercury, and some copper and zinc. The copper increases hardness and strength and the zinc acts as a scavenger during alloy manufacture, protecting major constituents from oxidation. Most dental alloys presently available contain 25 to 27% tin and consist mainly of the inter-metallic compound Ag and Sn. When porcelain veneers are added to gold alloys for high-grade dental restoration, 1% tin is added to the gold alloy to ensure bonding with the porcelain.

Titanium Alloys.

     Tin strengthens titanium alloys by forming solid solutions. Titanium can exist in the low-temperature alpha phase or the higher-temperature beta phase, which remains stable up to the melting point. In titanium alloys, relative amounts of alpha and beta phases present at the service temperature have profound effects on properties. Aluminum additions raise the transformation temperature and stabilize the alpha phase, but may cause embrittlement in amounts greater than 7%. However, with tin additions, increased strength without embrittlement can be obtained in aluminum-stabilized alpha titanium alloys. Optimum strength and workability can be obtained with 5% aluminum and 2.5% tin; in addition, this alloy has the advantage of being weldable.

     Lead is not found free in nature but Galena (lead sulfide) was used as an eye paint by the ancient Egyptians. Galena has a very metallic looking appearance and was, therefore, likely to attract the attention of early metalworkers. The production of metallic lead from its ore is relatively easy and could have been produced by reduction of Galena in a camp fire. The melting point of lead is 327C, therefore, it would easily flow to the lowest point in the fireplace and collect. At first lead was not used widely because it was too ductile and the first uses of lead were around 3500 B.C.. Lead's use as a container and conduit was important and lead pipes bearing the insignia of Roman emperors can still be found. Lead is highly malleable, ductile and non-corrosive making it an excellent piping material. Its symbol is Pb from the latin plumbum.

     The ability of lead to flow and collect at the bottom of the campfire is an important concept in process metallurgy as reduction reactions to be useful must cause a phase separation between the metal and the gangue. Also, the phase separation should also enable the metal to be cast into a desired shape once concentrated.

     Smelted copper was rarely pure, in fact, it is clear that by 2500 BC the Sumerians had recognized that if different ores were blended together in the smelting process, a different type of copper, which flowed more easily, was stronger after forming and was easy to cast, could be made. An axe head from 2500 BC revealed that it contained 11% tin and 89% copper. This was of course the discovery of Bronze. However, by 2000 BC copper implements contained very little tin as local reserves of tin had been exhausted. The Sumerians were forced to travel to find the necessary ores. Bronze was a much more useful alloy than copper as farm implements and weapons could be made from it, however, it needed the discovery of tin to become the alloy of choice.

     Native Tin is not found in nature. The first tin artifacts date back to 2000 B.C., however, it was not until 1800 B.C. that tin smelting became common in western Asia. Tin was reduced by charcoal and at first was thought to be a form of lead. The Romans referred to both tin and lead as plumbum where lead was plumbum nigrum and tin was plumbum candidum. Tin was rarely used on its own and was most commonly alloyed to copper to form bronze. The most common form of tin ore is the oxide casserite. By 1400 BC. bronze was the predominant metal alloy. Tin's symbol is Sn from the stannum.

     Tin is highly malleable and ductile and has two allotropic forms which lead to tin initially having its own disease (tin pest or blight) which was actually formation of alpha-tin below 13 C. As alpha-tin is a highly friable cubic structure with a greater specific volume than beta-tin, during the phase change, which is kinetically limited, nodules of alpha-tin become visible on the surface of beta-tin giving rise to early belief of sickness and the first true doctors of metallurgy. Tin is highly crystalline and during deformation is subject to mechanical twinning and an audible tin cry. Tin is also quite resistant to corrosion.

     Tin is found as vein tin or stream tin. The tin ore is stannic oxide and is generally found with quartz, feldspar or mica. The ore is a hard, heavy and inert substance and is generally found as outcroppings as softer impurities are washed away.

Top