Most metals conduct heat and electricity well and many common metals can be mixed together to form alloys – substances with properties different from those of the parent metals but more useful in particular applications. Primitive man was not aware of many properties of metals, yet appreciated their toughness and durability, their hardness, and their ability to be worked into almost any desired shape. It was also found that some metals retain an untarnishable luster. Because of this, and their attractive appearance and rarity, these metals were used for money and personal adornment and became known as "precious".

 

Early steps in metallurgy

Civilized people of 6,000 years ago had learned to work with gold, copper, silver, and probably tin. The earliest metallurgy stemmed from the discovery of native metals (which occurred naturally in their metallic state), but gradually man learned how to extract metals from minerals – metallic compounds – by heating them in a furnace, usually in the presence of charcoal. By about AD 1400 water-driven bellows could make a furnace so hot that even iron could be smelted.

 

Once metal could be melted it could be cast by pouring it as a white-hot liquid into a mold and leaving it to cool. Gradually men learned how to make more complicated molds, designed to open so that the cast object could be extracted. But the most important early method of shaping metals was forging. The metal is not melted, but merely softened by being heated to a bright orange; then it is shaped by blows from a hammer. The smith (Figure 1) developed the anvil and an increasing range of shaped tools for hammering against hot metal (Figure 6). He learned to know the quality of metal by eye, to judge its exact temperature and to shape it accurately before it cooled. Medieval swordsmiths had to fashion blades that were hard (and therefore tended to be brittle) on the outside, to take a keen cutting edge, yet tough and supple inside.

 

This selection of smith's products was typical of customer needs in Western countries in 1200–1850, during which period designs changed slowly. Door hinges (A) could be made on a small scale in brass for decorative casket. An idle back (B) suspended a kettle over the hearth and could be tipped to pour the boiling water safely. A horseshoe (C) was an item made by the millions in distinct family designs that often reveal the place and time of manufacture. A lamp (D) could be pinned or screwed to a house wall and was an item on which the smith could demonstrate his skill with fine wrought ironwork. The 17th-century Kentish plough (E) is still wooden but incorporates vital iron components.

 

Over the centuries a host of familiar objects gradually matured, differing from one region or country to another but each serving its purpose. Knives, plowshares, horseshoes, door hinges, clasps, roasting spits, fire-irons, and spurs were typical everyday objects made with no prior drawing or measurement but simply by skill and experience. The art of the jeweller also relied wholly on the craftsman's experience (Figure 4) and on his manual dexterity in fashioning objects that were both valuable and delicate.

 

It was in the making of jewelry that men first used the technique of soldering (Fig 5), in which a special alloy with a low melting-point is used to join other metal parts. It was also in jewelry that metals were first beaten out into thin wires, although during the Renaissance a way was found to "draw" wire by pulling it through a small hole.

 

Drawing and welding

The ability to be drawn is a characteristic of metals, stemming from their tensile strength and ductility (ability to change shape without breaking). Because the earliest metals were all fairly soft unless specially treated, for example as sword edges, they could be readily cut and pierced. This had to be done hot with large items, but small objects could be shaped cold. The most delicate work of all was the beautiful technique of inlaying patterns of one metal into recesses in another metal of contrasting color. Sometimes the inlaid pieces were secured by hammering the edges of the recesses. But in other cases soldering or brazing was employed, the latter using a brass (an alloy of copper and zinc), which was melted and run into the joints.

 

By 1800 the technique of welding metals using a hot gas flame was being developed and by the end of the century it had reached a high degree of perfection and been supplemented be welding with an electric arc. Welding, in which some of the metal is melted, exerts a profound effect on the metal's properties and much patient research was needed to find the best methods while simultaneously avoiding distortion caused by the severe heating.

 

The value of hand tools

Craftsmen using hand tools with the manual skill and judgment born of experience often provide the most efficient solution to many metalworking problems, especially where tasks are essentially creative or the objects made to individual order.

 

The same is true in countless jobs in which metalworking plays a part, such as building construction, plumbing, farming, motor bodybuilding and repair, and in what have become known as do-it-yourself handyman tasks about the home. A special part is played by artists who work with metal, either in creating jewelry or in the larger forms grouped under the heading of sculpture (Figure 3).

 

Most of these tasks involve some form of joining, such as welding or soldering, and a few require a forge. All hand tools such as shears, hacksaws and files to cut, shape and trim metal while cold. In nearly every case the precise dimensions are unimportant, provided that mating parts fit precisely. Even a watch-repairer normally works either by inserting a standard new part or making existing parts fit by eye and by feel. In modern manufacturing industry, however, the aims are entirely different. Mass-production of successive identical items usually calls for metalworking machines instead of slower human craftsmen.

 

Riveting is a method of joining metals without melting them. A hole is drilled through the parts to be joined (A) and a hot rivet passed through it (B). The end of the rivet is beaten with a ball-peen hammer (C) until it flattens over, making a tight join (D). Large structures such as girders and plating on ships' hulls can also be joined using rivets and mechanical hammers.