Materials and Techniques
Sculpture can be made from almost any organic or inorganic substance. The processes specific to making sculpture date from antiquity and, up to the 20th century, underwent only minor variations. These processes can be classified according to materials stone, metal, clay, and wood; the methods used are carving, modelling, and casting. In the 20th century the field of sculpture has been enormously broadened and enriched by new techniques, such as welding and assemblage, and by new materials resulting from technology, such as neon tubing.
Carving
A procedure dating from prehistoric times, carving is a time-consuming and painstaking process in which the artist subtracts, or cuts away, superfluous material until the desired form is reached. The material is usually hard and frequently weighty; generally, the design is compact and is governed by the nature of the material. For example, the narrow dimensions of the marble block used by Michelangelo to carve his David (1501-4, Accademia, Florence, Italy) strongly affected the pose and restricted the figure's outward movement into space.
Various tools are used, depending on the material to be carved and the state to which the work has progressed. In the case of stone, the rough first cutting to achieve the general shape may be performed by an artisan assistant using sharp tools such as points or punches for removing large chunks of stone at early stages of carving, these tools also pulverize the stone. Then the sculptor continues the work of cutting and chiseling using gouges or chisels. As work progresses, less penetrating tools are used, such as a file and a rasp; finishing touches are carried out with fine rasps; then by rubbing with pumice, emery or sand (abrasives), and - if a great degree of smoothness is desiredby adding a transparent patina, made with an oil or wax base.
A drill can be used where necessary to remove the stone to some depth; it became an
indispensable tool from the Renaissance to the 19th century when the pointing systems
required the drilling of holes in the block corresponding to measured positions on a model.
(pointing system developed to transfer from a plaster or clay model to a marble block)
A historical note
Early Greek statues are worked directly onto the block; sculptors worked in from each side carving away one layer at a time and always keeping the appearance of the whole in mind, similar methods were used by the Egyptians of 2000 years earlier.
Little is known about carving techniques in the Middle Ages
The Italian Renaissance started to be interested in carving as antique sculptures were excavated. The Greek method of working round the block, which was followed by Donatello, was abandoned by Michelangelo who carved the block from one side.
The works of Mannerists show sculptures presenting many viewpoints rather than the static
viewpoint that characterized early Renaissance works. Bernini had escaped from the Renaissance concept of the figure being found within the block, and the movement and torsion in his sculpture often necessitated the use of more than one block. (figura serpentinata)
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In 18th and 19th century mechanical methods of transferring from models assumed greater importance e.g. Rodain only worked in clay and never touched marble, the transfer from his models was executed by his assistants.
The 20th century has seen a return by artists such as Henry Moore to methods of direct carving.
Many materials have been used as the base for carving; stone, limewood, ivory, marble.
Modelling
Modelling consists of addition to, or building up of, form. The materials used are soft and yielding and can be easily shaped, enabling rapid execution. Thus, a sculptor can capture and record fleeting impressions much the way a painter does in a quick sketch. Clay or claylike substances, baked to achieve increased durability, have been used for modelling since ancient times.
Models may be prepared as finished expressions of an artist`s idea or, more commonly, as preparatory works for the other branches of sculpture.
There are two types of model used as preparation for casting and carving:
- pensieri in which the composition of the figure is worked out
- full-sized models - which can be transferred to marble block or cast in bronze.
For small models made in clay, armature is not used as this can cause the clay to crack; wood can swell from water in the clay, and iron can rust for the same reason.
However, full-sized clay models are executed with wood armature, necessary to support the weight of the figure. To prevent the clay from cracking, cloth cuttings or horsehair are added, and also some baked flour to prevent the clay from drying too quickly.
Drapery may be made by applying material dipped in clay to the figure.
Casting
The only means of obtaining permanence for a modeled work is to cast it in bronze or some other durable substance. Small statues may be cast in solid bronze but the enormous weight of a large bronze statue and the amount of metal required for its manufacture encouraged the development of systems for hollow casting in which the statue has a thin shell of metal surrounding a solid core of noncombustible material.
Two methods of casting are used: the cire perdue, or lost-wax process, and sand-casting. Both methods have been used since antiquity, although the lost-wax process is more widely employed. Casting is accomplished in two stages: First, an impression or negative mould is formed from the originala clay model, for instanceand second, a positive cast or reproduction is made of the original work from the negative impression. The term negative refers to the hollow form or mould into which the liquefied casting material is poured. The term positive means the copy or reproduction resulting from filling the negative mould with the substances selected for the specific cast, which are then allowed to harden. Plaster is frequently used for the negative mould, and bronze for the positive or final work.
After casting, superfluous bronze is removed and the surface is polished with abrasives like pumice. Initially bronze is red but it turns black as it ages.
Construction and Assemblage
Although traditional techniques are still employed, much 20th-century sculpture is created by construction and assemblage. These methods have their origin in collage, a painting technique devised by Pablo Picasso and the French artist Georges Braque in 1912, in which paper and foreign materials are pasted to a picture surface. Picasso also made three-dimensional objects such as musical instruments out of paper and scraps of diverse materials, which were termed constructions. Examples of modern constructivist sculpture range from the surrealistic boxes of Joseph Cornell to the junk-car and machine-part works of John Chamberlain, both Americans. The term assemblage, which is now sometimes used interchangeably with construction, was coined by the French painter Jean Dubuffet to refer to his own work, which grew out of collage.
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