Metals

The nature of metals

The atoms which make up metals are bonded in a way that is peculiar to metals. A metal becomes a solid at a certain temperature; and the atoms of the metal settle into a characteristic, well ordered configuration. In this configuration the atoms are fixed rigidly in relation to each other. The configuration is called a crystal lattice or a crystal.

Some of the basic qualities of metals include the following:

• they are good conductors of heat and electricity;

• high reflectivity when their surfaces are smooth;

• usually good ductility, that is, they are capable of being drawn out into wire or threads;

• good malleability, that is, they can be extended or shaped by hammering or by pressure with rollers; and

• mechanical strength.

Alloys

For centuries, the properties of metals—such as their appearance, strength, malleability and chemical reactivity—have been altered by combining them. These combinations are called alloys. For example, iron combined with carbon produces alloys such as cast iron and steel; whereas the alloying of chromium and nickel with iron forms stainless steel.

Similarly, copper can be combined with zinc, to form brass; and with tin, to form bronze.

Patina

• exposure to the elements; and

• deliberate steps taken to produce this effect. For example, sculptors often apply chemicals to the surface of a work, to produce a certain visual effect with the corrosion products.

Before any decision is made to remove this layer of corrosion products from an object, the nature of the object and its history must be considered very carefully. For instance, under no circumstances should the patina be removed from an ancient bronze sculpture, whereas a Victorian-era silver candelabra would have been highly polished and so should be cleaned of accumulated tarnish.

Examples of copper alloy Japanese sword handles, where the patina is an integral part of the object. Photograph courtesy of the Western Australian Museum