To withstand the stresses of firing, a large pottery sculpture must be hollow and of an even thickness. There are two main ways of achieving this. In the process of hollow modeling, which is typical of the potter’s approach to form, the main forms of the clay model are built up directly as hollow forms with walls of a roughly even thickness. The methods of building are similar to those employed for making hand-built pottery—coiling, pinching, and slabbing. The smaller forms and details are then added, and the finished work is allowed to dry out slowly and thoroughly before firing. The process of solid modeling is more typical of the sculptor’s traditional approach to form. The sculpture is modeled in solid clay, sometimes over a carefully considered armature, by the sculptor’s usual methods of clay modeling. Then it is cut open and hollowed out, and the armature, if there is one, is removed. The pieces are then rejoined and the work is dried out and fired. General characteristics of modeled sculpture
The process of modeling affects the design of sculpture in three important ways. First, the forms of the sculpture tend to be ordered from the inside. There are no external containing forms and planes, as in carved sculpture. The overall design of the work—its main volumes, proportions, and axial arrangement—is determined by the underlying forms; and the smaller forms, surface modeling, and decorative details are all formed around and sustained by this underlying structure. Second, because its extension into space is not limited by the dimensions of a block of material, modeled sculpture tends to be much freer and more expansive in its spatial design than carved sculpture. If the tensile strength of metal is to be exploited in the finished work, there is almost unlimited freedom; designs for brittle materials such as concrete or plaster are more limited. Third, the plasticity of clay and wax encourages a fluent, immediate kind of manipulation, and many sculptors, such as Auguste Rodin, Giacomo Manzù, and Sir Jacob Epstein, like to preserve this record of their direct handling of the medium in their finished work. Their approach contrasts with that of the Benin and Indian bronze sculptors, who refined the surfaces of their work to remove all traces of personal “handwriting.” Constructing and assembling
A constructed or assembled sculpture is made by joining preformed pieces of material. It differs radically in principle from carved and modeled sculpture, both of which are fabricated out of a homogeneous mass of material. Constructed sculpture is made out of such basic preformed components as metal tubes, rods, plates, bars, and sheets; wooden laths, planks, dowels, and blocks; laminated timbers and chipboards; sheets of Perspex, Formica, and glass; fabrics; and wires and threads. These are cut to various sizes and may be either shaped before they are assembled or used as they are. The term assemblage is usually reserved for constructed sculpture that incorporates any of a vast array of ready-made, so-called found objects, such as old boilers, typewriters, engine components, mirrors, chairs, and table legs and other bits of old furniture. Numerous techniques are employed for joining these components, most of them derived from crafts other than traditional sculptural ones; for example, metal welding and brazing, wood joinery, bolting, screwing, riveting, nailing, and bonding with new powerful adhesives.
The use of constructional techniques to produce sculpture is the main technical development of the art in recent years. Among the reasons for its popularity are that it lends itself readily to an emphasis on the spatial aspects of sculpture that preoccupied so many 20th-century artists; it is quicker than carving and modeling; it is considered by many sculptors and critics to be especially appropriate to a technological civilization; it is opening up new fields of imagery and new types of symbolism and form.
For constructed “gallery” sculpture, almost any materials and techniques are likely to be used, and the products are often extremely ephemeral. But architectural sculpture, outdoor sculpture, and indeed any sculpture that is actually used must be constructed in a safe and at least reasonably permanent manner. The materials and techniques employed are therefore somewhat restricted. Metal sculpture constructed by riveting, bolting, and, above all, welding and brazing is best for outdoor use. Direct metal sculpture
The introduction of the oxyacetylene welding torch as a sculptor’s tool has revolutionized metal sculpture in recent years. A combination of welding and forging techniques was pioneered by the Spanish sculptor Julio González around 1930; and during the 1940s and 1950s it became a major sculptural technique, particularly in Britain and in the United States, where its greatest exponent was David Smith. In the 1960s and early 1970s, more sophisticated electric welding processes were replacing flame welding.
Welding equipment can be used for joining and cutting metal. A welded joint is made by melting and fusing together the surfaces of two pieces of metal, usually with the addition of a small quantity of the same metal as a filler. The metal most widely used for welded sculpture is mild steel, but other metals can be welded. In a brazed joint, the parent metals are not actually fused together but are joined by an alloy that melts at a lower temperature than the parent metals. Brazing is particularly useful for making joints between different kinds of metal, which cannot be done by welding, and for joining nonferrous metals. Forging is the direct shaping of metal by bending, hammering, and cutting.
Direct metalworking techniques have opened up whole new ranges of form to the sculptor—open skeletal structures, linear and highly extended forms, and complex, curved sheet forms. Constructed metal sculpture may be precise and clean, as that of Minimalist sculptors Donald Judd and Phillip King, or it may exploit the textural effects of molten metal in a free, “romantic” manner. Reproduction and surface-finishing techniques
Casting and molding processes are used in sculpture either for making copies of existing sculpture or as essential stages in the production of a finished work. Numerous materials are used for making molds and casts, and some of the methods are complex and highly skilled. Only a broad outline of the principal methods can be given here. Casting and molding
These are used for producing a single cast from a soft, plastic original, usually clay. They are especially useful for producing master casts for subsequent reproduction in metal. The basic procedure is as follows. First, the mold is built up in liquid plaster over the original clay model; for casting reliefs, a one-piece mold may be sufficient, but for sculpture in the round a mold in at least two sections is required. Second, when the plaster is set, the mold is divided and removed from the clay model. Third, the mold is cleaned, reassembled, and filled with a self-setting material such as plaster, concrete, or fibreglass-reinforced resin. Fourth, the mold is carefully chipped away from the cast. This involves the destruction of the mold—hence the term “waste” mold. The order of reassembling and filling the mold may be reversed; fibreglass and resin, for example, are “laid up” in the mold pieces before they are reassembled.
Plaster piece molds are used for producing more than one cast from a soft or rigid original and are especially good for reproducing existing sculpture and for slip casting (see below). Before the invention of flexible molds (see below), piece molds were used for producing wax casts for metal casting by the lost-wax process. A piece mold is built up in sections that can be withdrawn from the original model without damaging it. The number of sections depends on the complexity of the form and on the amount of undercutting; tens, or even hundreds, of pieces may be required for really large, complex works. The mold sections are carefully keyed together and supported by a plaster case. When the mold has been filled, it can be removed section by section from the cast and used again. Piece molding is a highly skilled and laborious process.