Bronze is an alloy of copper and tin, and often also contains lead or zinc. It is strong and durable but can also capture the fine, complex detail within a casting mould. The term 'bronze' is often used for other metals, including brass, which is an alloy of copper and zinc.
Bronze has been used in Europe since antiquity to produce tools, weapons, sculpture and decorative works. This continued throughout the medieval period. In the 15th century there was then a deliberate revival of the forms and techniques of ancient Greece and Rome.
There are two basic methods of casting a bronze. Sand casting is a simple technique that uses moulds made of compact, fine sand. Lost-wax casting is a complex process using wax models.
In the 'direct' method, the original wax model is used and therefore destroyed. In the 'indirect' method, plaster moulds are taken from the original wax. These can then be reused many times.
Video: How was it made? Lost wax casting
For centuries sculptors have used stone for figurative carvings and ornamental architectural work. Different types of stone were used in different regions, with sculptors generally using geologically local materials available nearby. Marble was used in Italy and exported to northern Europe from about 1550 onwards. It is a particularly brittle stone, which is why supports are often used to connect extremities to the main part of the sculpture. It was usually the intention to remove these once the statue was installed, although this was not always done. Different types of limestone were employed all over Europe, and alabaster was popular in England, northern France, the Netherlands, Germany and Spain.
The heaviness of stone makes stability an important consideration. Many free-standing marble figures in dynamic poses are portrayed with tree trunks or columns attached to the legs in order to provide a stable base. Figures to be displayed in niches were often hollowed out to reduce their weight.
The tools used for stone-carving have remained more or less unchanged since antiquity. A mason’s axe is used to cut out the basic shape of the sculpture, which is then roughed out using picks, points and punches struck by a hammer or mallet. Different sizes of tool are used throughout the carving process, each leaving their mark. Roughing out tools leave deep, uneven grooves whereas flat chisels achieve finer results and are used as a surface finishing tool for sandstone, limestone and marble. A flat chisel struck at an angle of 45 degrees (the ‘mason’s stroke’) leaves a ridged channel, and its edge can be used to define lines. Claw chisels have serrated edges that mean they arc capable of rapid but controlled removal of material. Drills are used to excavate the stone, and can also be used to create decorative effects.
Further smoothing is achieved using rasps or rifflers (metal tools with rough surfaces) or minerals such as sand or emery (stone grit). Polishes can then be applied to sculpture of fine-grained stone after it has been abraded. Marble and alabaster were polished with pumice, producing a smooth, translucent and reflective surface, though the surface could also be left partially unpolished in order to create a variety of textures.
Regional availability played a large part in determining which wood was chosen for a sculpture, though the properties of individual trees was also a factor. The hardness of a wood depends on the density of its grain. Softwoods from evergreens such as cedar and pine are coarser, less dense and easier to carve, whereas hardwoods from deciduous trees such as oak, boxwood, walnut and limewood, are harder but more durable and allow more elaborate carving and finer details.
In southern Germany, sculptors favoured limewood, but oak was more widely used in northern Germany, the Netherlands, northern France and England. Walnut was used in Burgundy and France, but in Italy, Spain and the Alpine regions pine or poplar were more popular.
Wood is carved in a similar way to stone. The design is drawn on a split tree-trunk, the size of which usually determines the dimensions of the finished sculpture, though extra sections can be pieced in. The form of the sculpture is roughly carved with a broad axe and then shaped with tools such as the narrow axe, flat-headed chisels, gouges and skew-bladed firmers (a kind of chisel with a hooked end used for cutting folds in drapery). After carving, the surface is normally smoothed with sandpaper or other abrasives.
Wood naturally contains moisture when first felled and can re-absorb it later in damp conditions. Cracks usually follow the grain of the wood and are caused when parts dry at different rates. Sculptors therefore try to minimize cracking by removing all superfluous wood, especially the heartwood at the centre of a log. Another cause of damage to wooden sculpture is woodworm. The holes and burrows that woodworm causes are often visible on the surface of older pieces.
Wood sculptors often cooperated with painters as wood sculpture was sometimes painted or decorated with gilding, or embellished with glass or semi-precious stones. At the end of the fifteenth century limewood sculptors in southern Germany produced unpainted wood sculpture. Although these sculptures were not painted, they were coated with transparent glazes, sometimes tinted brown.
Ivory is the dense, hard, creamy white substance that forms the tusks of mammals, though the term is also used for other similar materials. For centuries it has been highly valued by craftsmen and patrons alike for use in religious and secular objects.
The main source of ivory is elephant tusks from North Africa and India. The tusks of the Atlantic walrus and whalebone from the Finner whale have been popular in western and northern Europe since the 10th century. Animal bones were used by the Embriachi workshop in northern Italy during the 15th century.
The structure of ivory varies from one species of animal to another. Elephant tusks grow outward in successive layers and have a conical interior cavity (the 'pulp cavity'). This extends into a very small nerve running the length of the tusk. African ivory tusks can grow as long as two metres.
Carving in semi-precious stone & shell
Specialist craftsmen used a wide variety of materials for carvings. These ranged from gemstones and hardstones like rock crystal to softer organic materials such as shell, coral and mother-of-pearl.
Hardstones were worked with metal tools, diamond drills and abrasive powders. Organic materials, and the softer mineral substances like jet and amber, were carved with a variety of knives and chisels. Some of these materials, among them jet and coral, were believed to have magical or medicinal powers, whereas rock crystal symbolised light and purity in medieval times. These carvings had many functions. They included cameo portraits, gems with mythological subjects, religious artefacts such as devotional pendants, containers carved in precious rock crystal and inexpensive pilgrimage badges made of jet.
Also, from about 1540-60 rulers and wealthy burghers assembled collections of gems, cameos and other virtuoso carvings. They often displayed them in special cabinets, or rooms, alongside curiosities from the natural world and foreign parts.
Shell cameos are much easier to cut than those made from gemstones. Also, the raw material is cheaper and easier to acquire. They were popular in the 16th century and then again in the 18th and 19th centuries, when the passion for carved gemstones led to a parallel explosion in the market for cheaper shell cameos. They are still popular today.
Modelling in clay
Clay is a very versatile raw material. It is relatively cheap and widely available. It can be modelled by the sculptor to form a unique object, or moulded by workshops for mass production. Sculptors often made rapid sketches in clay to capture initial ideas and then developed more finished models to show to patrons. They also used clay models when transferring compositions into more permanent materials such as marble. Clay can also be pressed into moulds, enabling multiple copies to be made.
Modelling marks are not usually visible in finished pieces of ceramic sculpture but can often be seen in ceramic models made for sculpture in other media. Typical are rough, uneven grooves and ridges caused when clay is pushed to one side as marks are made.
Fired clay is known as 'terracotta' (cooked earth). The firing irreversibly changes the clay, making it stronger and capable of receiving a variety of surface finishes. Clay models were sometimes fired to preserve them. Large European works, such as the ‘stemma’ or coat of arms, made by Luca della Robbia for King Rene of Anjou, were cut into pieces with cheesewire in order to fit into the kiln, and joined together after firing.Explore clay objects in Search the Collections
Wax models are original and unique creations that were sometimes works of art in their own right and sometimes an intermediary stage in the sculptural process. Many bronze sculptures, for example, are cast from models that were first made in wax, involving a highly skilled process known as lost-wax casting.
Audio: How did sculptors make wax models?
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The rough surface of European limestone and sandstone sculptures was usually concealed by paint, gilding, or inlaid glass or semi-precious stones. Marble sculpture was rarely decorated because a plain white surface like those of classical Greek and Roman marble sculptures was considered the most desirable finish. In fact these classical sculptures would probably have originally been painted, but by the time they were rediscovered in post-classical times, the paint had worn away.
Wood sculpture was also painted, gilded, or decorated with incised and punched patterns and occasionally inset glass, though at the end of the 15th century, sculptors in southern Germany produced unpainted limewood sculptures.
The appearance of bronze sculptures could also vary, according to the particular alloy used and the surface treatment. Chemical and organic lacquers can produce a variety of colours including black, green and reddish-brown. Bronzes could also be gilded, sometimes using the fire-gilding method. In this process a paste of milled gold and mercury is spread over the sculpture which is then heated, fusing the gold to the surface and driving off the mercury. Fire-gilding is now outlawed in most countries due to the toxicity of mercury vapour. Gold lacquer can also be used to give a gilded appearance, though it is less permanent than fire-gilding.
In Renaissance Italy, terracotta (fired clay) sculptures were usually coloured. In the 15th century, Luca della Robbia, a sculptor from Florence (1399/1400-1482), developed a method of tin-glazing terracotta sculpture that had previously only been used on pottery. Della Robbia's method used pigment suspended in a tin-oxide glaze rather than painted onto slip. The resulting enamelled terracottas were particularly durable and had an attractive, bright and reflective, surface. By the late 18th century however, unglazed terracotta had become popular with many European artists such as the French sculptor Clodion (1738-1814).