A very useful book to find definitions of sculpture techniques is:
Jane BASSETT and Peggy FOGELMAN, Looking at European Sculpture. A Guide to technical terms, The J. Paul Getty Museum in collaboration with The Victoria and Albert Museum, 2007.
The authors kindly allowed me to quote some of their entries. I am happy to thank them.
A bronze sculpture cast using MOLDS taken from a pre-existing work in bronze rather than from the original MODEL.
An aftercast is later in date and slightly smaller than the bronze from which it was derived; the reduction in dimensions in the aftercast occurs because molten metal shrinks as it cools. The process of taking molds from an existing bronze may result in the softening or loss of surface detail. Although this deficiency can be somewhat compensated for by careful CHASING, it nevertheless explains why aftercasts are usually considered to be of diminished quality. See also LOST WAX CASTING. (p. 7)
An internal skeleton, usually of metal or wood, which supports a sculpture in clay, plaster, or other modeling material during its construction.
Metal armatures are also used as internal supports for large metal monuments. The armature usually consists of a central, rigid element onto which the main mass of the sculpture is MODELED. Wires or padding are attached to the central component to support projecting forms such as limbs. An armature serves both to bear the weight of the sculpture and to maintain the positions and forms of the compositional elements as the sculpting material hardens. In LOST WAX CASTING, the armature, which extends from the base up into part or all of the sculpted composition, should be distinguished from the core supports, which are separate, shorter pieces of wire or rod added to strengthen isolated sections of the core. Metal armatures in clay sculptures are always removed before firing, since expansion of the metal as it is heated will cause the clay to crack. In order to reduce the weight of cast bronze sculptures, metal armatures used in the build-up of the core are often removed after casting, when the support is no longer needed. On the other hand, armatures contained in plaster and wax sculptures are not easily removed and add needed strength to the finished work. Iron armatures left in sculpture can be the cause of damage due to rusting of the iron. When present, armature remnants can be detected through the use of radiography (X-rays). (p. 10)
See LOST WAX CASTING and SAND CASTING.
You can also consult or watch:
Élisabeth Lebon, Dictionnaire des fondeurs de bronze d'art, France 1890-1950, Perth, Marjon éditions, 2003: http://dico.fondeursdart.free.fr/lebon.html
Élisabeth Lebon, Fonte au sable – Fonte à la cire perdue. Histoire d’une rivalité, Paris, INHA-Ophrys, 2012: http://inha.revues.org/3243
Adrian de Vries’s Bronze Casting Technique: http://www.getty.edu/art/gettyguide/videoDetails?segid=437 (video, duration: 8:38)
Casting Bronzes: http://www.getty.edu/art/gettyguide/videoDetails?segid=370 (video, duration: 6:10)
Coating a surface to give it the appearance of bronze, generally through the application of metallic powders (usually copper or copper alloys such as brass); the powder may be mixed into a paint medium such as linseed oil and brushed on, or the surface may be coated with a tacky substance and the powder dusted on.
A work made of an inexpensive material like wood might be treated to look like cast bronze, and artists frequently bronzed their preparatory plaster models as a means of approximating the appearance of the final cast bronze. Plaster casts of finished sculptures were often bronzed and served as inexpensive reproductions which were popular in the nineteenth century. The term bronzing is sometimes used to refer to the coating of a surface with bronze or copper leaf or to ELECTROPLATING a surface with a copper alloy. (p. 13)
The removal of material to reveal a form, a process often contrasted with MODELING, which involves the addition of material to build a form.
Among the most popular European carving materials from the Renaissance through the nineteenth century were marble, wood and ivory. The hand tools and techniques used to carve these materials have changed little since antiquity and essentially involve the application of force to a sharpened cutting edge.
Marble carvers use drills as well as a variety of iron tools, which are struck with heavy mallets or, since the early twentieth century, powered by compressed air.
Wood can be carved by applying hand pressure on knives, chisels, and gouges, by striking chisels and gouges with wooden mallets, or by filing or drilling.
The tools and techniques for carving ivory are similar to those for wood, but levered scraping tools and files are more commonly employed.
Although plaster and clay sculptures are often built by modeling or casting, their surfaces can be carved once the material has begun to harden. (p. 16)
To understand the genesis of a carved sculpture, you can look at the film The Genesis of a Sculpture, by Adam-Tessier, directed by Olivier Clouzot and Julien Pappe (13 minutes, black and white), part of The Roland Collection of Films on Art (www.rolandcollection.com, free clip, small fee for complete film download).
Or: Carving Marbles with Traditional Tools: http://www.getty.edu/art/gettyguide/videoDetails?segid=4219 (video, duration: 2:48)
A term encompassing two processes in metal working: first, the MODELING of decorative patterns on a hand-shaped sheet-metal surface using punches applied to the front, usually in combination with repoussé, a technique in which the back is hammered to create a raised relief on the front; and second, the finishing and refinement of a cast sculpture.
The initial stage of chasing a cast bronze sculpture is sometimes called fettling, which includes scrubbing the surface to remove the black oxide layer, as well as removing the sprues and vents, and the fins or flashes resulting from cracks and joins in the mold, by sawing, filing, and chiseling. The core, core pins, and ARMATURE are often removed if possible, the core pin holes and casting flaws are filled with plugs or cast-in repairs, and separately cast elements are joined together. The next chasing step involves the finer tooling of the surface, including: hammering to hide added plugs and repairs; sharpening or adding details using chisels and punches; wire brushing to give an even, light-catching striation to the surface; and polishing in selected areas using a variety of abrasives, scrapers, or burnishers. The chasing of a sculpture requires tremendous skill and time, and its level of quality varies greatly with each artist. (p. 19-21)
(French, "Lost wax")
See LOST WAX CASTING.
The intentional production of a sculpture in several virtually identical examples.
In sculpture, the term edition is usually associated with bronze casting and signifies the execution of multiple casts from the same set of MOLDS, which derive from the original MODEL. The resulting bronzes, sometimes called replicas, are substantially the same in size, form, and composition. The repeated use of the same molds ensures consistency among the bronzes in the edition, but slight variations occur due to castings flaws, to differences in CHASING (if the finishing of each bronze is entrusted to a different foundry assistant), or to deterioration of the molds. An edition is usually limited to a certain number of casts; the size of an edition may be determined by either the artist or the foundry, depending upon the nature and purpose of the commission. Although multiple casts of bronzes were executed as early as the late fifteenth century, the widespread production of bronzes in large editions began in the nineteenth century. (p. 32)
The process of applying a metal coating to a surface by means of an electric current.
The surface to be coated is submerged in a bath containing an electrolyte solution and a solid piece of the plating metal. An electric current is applied to the bath, causing the plating metal to dissolve and deposit onto the surface to be coated. That surface must be electrically conductive; it can be metal, or a material such as wood, plaster, or wax that has been made conductive by coating it with graphite or a metallic powder. Although pure metals such as silver, gold, and copper are most easily deposited, electroplating alloys such as brass is also possible. Since they are difficult to chemically patinate, electroplated surfaces are frequently coated with colored lacquers (see PATINA). Electroplating was discovered in the early nineteenth century and came into common use in the 1840s. (p. 32)
The process of using an electric current to deposit metal into a mold or negative impression of a desired form, in order to create a three-dimensional relief.
A similar technique, electroforming, builds a metal shell onto a positive pattern. The mold or pattern can be made of wax or plaster coated with an electrically conductive material such as graphite. The process is similar to ELECTROPLATING, but with different results, since electrotyping creates a metal shell rather than a surface coating. Electrotypes were often backed with other metals such as lead to strengthen the shell and make them as heavy as a cast sculpture. An electrotype is sometimes distinguishable from a LOST WAX or SAND CAST sculpture by its very even and often thin walls. An electrotype made of a less expensive material, like copper, can be electroplated with silver or gold to give the impression of a solid silver or gold casting. Electrotyping was developed in the mid-nineteenth century and gave rise to the mass production of affordable works of art and decoration for the general public. (p. 32)
The establishment where metal casting takes place.
A LOST WAX foundry is dived into areas where the various functions are performed: a MOLD and wax making area; the casting area with a kiln or drying oven, a melting furnace (in which metals are melted and alloyed), and a casting pit; and a CHASING and PATINATION area. Because of the expense and experience needed to run a foundry, as well as local guild restrictions, artists often entrusted the casting of their models to professional founders rather than establishing foundries within their own workshops. (p. 37-38)
A general term describing identification marks added to a cast sculpture by the FOUNDRY.
Foundry stamps may indicate the name of the foundry or founder, the date of execution, and/or the EDITION number. The stamp may be pressed or carved into the wax MODEL or the core before casting or incised or stamped into the cast metal itself. (p. 38)
The process of coating an object with a thin layer of gold.
A surface which has been covered by gilding is said to be gilt or gilded. The term applies to a variety of techniques and is sometimes used in reference to other coatings meant to imitate gold, such as silver leaf, tin leaf, or palladium leaf (a non-tarnishing silver-colored metal) coated with gold-colored GLAZES; Dutch metal (brass leaf, also called schlag leaf and composition leaf); and "gold powders" made of gold-colored brass (see BRONZING).
As a decorative technique, the purpose of gilding is to create illusionistic effects. A sculpture that is completely gilded appears to be solid gold, while a partially gilded surface can imitate the appearance of other textures and materials. The term parcel gilt refers to partial gilding of selected elements. When silver leaf is employed for its own sake rather than to imitate gold, the term used is silver gilt, or silvering.
The three primary European techniques for applying gold to sculpture were leaf gilding, mercury gilding, and, after the mid-eighteenth century, ELECTROPLATING. (.../...) (p. 40)
In ceramic sculpture, a silica-based glassy coating fused to a ceramic body, which functions as both a decorative and a protective layer. In other polychrome sculpture, a colored transparent layer of resin applied over metal leaf or a painted surface (see GILDING).
Glazing over silver leaf could be used to give the appearance of gold or gemstones; in addition, the resin protects the silver leaf from tarnishing. Glazes applied over opaque paint layers lend a luminous quality to the underlying paint. Colorants used for resin glazes include dyes, pigments, and stains. (p. 42)
A location on a sculpture where two separate sections have been fitted together.
Because artists took great care to hide their joins, join lines are often detectable only through radiography (X-rays).
On metal sculpture, separate pieces can be joined mechanically by means of rivets, pins, screws, and dove-tailed joints, or by soldering, welding, or casting adjoining sections in place. (Metal sculptures created using the indirect LOST WAX CASTING technique require fewer metal joins as it is possible to use wax-to-wax joins to attach the separately cast wax sections.)
On wood sculpture, woodworking joins such as butt and mortise-and-tenon can be used in combination with glue and nails. The join lines in polychrome wood sculpture were often covered with cloth to obscure the gaps caused when the pieces expanded or contracted in different directions and at different rates. (p. 49)
An image made directly from a living subject or from MOLDS taken from that subject.
The term commonly refers to life-size reproductions of organisms, such as plants (e.g. fruits and grasses), small reptiles (e.g. lizzards and snakes), insects, and fish, which were made from the specimens themselves. "Life cast" should not be interpreted too literally, since the creatures would have been killed in order to prepare them for casting or the taking of molds. The resulting images appear extremely life-like and accurately record every detail of texture and anatomy. Historians disagree as to whether the practice originated in Italy, France, or Germany; the Italian tradition dates to at least the fourteenth century. In addition to serving as independent sculptures, specimens cast from nature frequently decorated metalwork and ceramic plates and vessels in the sixteenth and seventeenth centuries. Molds of human anatomy, such as the hands or face, can also be referred to as life casts when taken directly from a living subject. (p. 51-52)
LOST WAX CASTING
A technique that since antiquity, except for a period in the nineteenth century, has been the primary method for casting bronze sculpture.
In basic terms, lost wax casting involves replacement of a wax MODEL with molten bronze. When creating waxes for hollow casts, the wax can be formed in two ways: in the direct method, the wax is modeled directly onto a preformed core; in the indirect method, the wax is pressed or poured into a piece MOLD made from the original model (thus created indirectly), and the core material is then poured into the formed wax. Once the core-filled wax model has been completed by either the direct or indirect method, core pins are driven through the wax into the core and left projecting so that they will engage the outer part of the mold (the investment) and preserve the distance between the core and outer mold once the wax is gone. A circulatory system of channels made of wax is then added: sprues (or gates) to conduct metal into the mold cavity and vents (or risers) to conduct air and gases out of the mold cavity and core.
The sprued wax is then enclosed within the investment. The entire assemblage of core, wax model, and outer investment are heated to evaporate all moisture and to melt out the wax. The casting alloy is heated and poured into the mold, filling the spaces once occupied by the wax. When the metal has cooled, the cast sculpture is revealed by breaking away the investment. At this point, CHASING and the application of the PATINA can be carried out.
Lost wax casts are distinct from SAND CASTS in that their cast-in surface details are finer, and they are less likely to consist of separate sections that were joined after casting. The interior may show the impression of fingerprints or drips that were present in the wax.
Lost wax castings are generally more porous than sand castings because the core and investment material do not as readily absorb the released gases, which remain within the metal as bubbles that appear in radiographs (X-rays) as irregular shaped voids. (p. 54-56)
A method of manipulating a sculptural medium such as clay, plaster, or wax to create a form.
Modeling involves the building up and shaping of a pliable material, in contrast to CARVING, which involves cutting away a hard substance such as stone, wood, or ivory. Hands as well as hand tools, generally long, thin pieces of wood, metal, or ivory, with wire-loop or specially shaped ends, are used for modeling.
In art the term modeling also refers to the treatment of volumes in a sculpted composition and the degree of depth with which the facial features or anatomy of a figure are rendered. Deep modeling maximizes the play of light upon the projections and recesses of a sculpted surface and creates striking contrasts between highlights and shadows. Shallow modeling achieves a more unified but less dramatic surface. (p. 61-63)
The negative impression of a form into which a sculpting material is poured or pressed.
Types of molds include:
- intaglio molds, which are carved into stone or ceramic that is resistant to heat;
- piece molds, which can be taken apart without damage to the model, the cast sculpture, or themselves;
- waste molds, which must be broken away to reveal the cast sculpture and therefore can produce only a single casting;
- sand molds, used in SAND CASTING, which are relatively easy to make but must be remade after each use;
- flexible molds, made of gelatin (and today of various elastic polymers such as silicone), which can be used in place of piece or waste molds but may deteriorate;
- and finally, mother molds, which hold all the sections of a piece mold in proper alignment.
Molds allow for the production of one or many copies of an original model or sculpture. Essentially all major European metal sculpture from the fifteenth through the nineteenth century was cast (or, in the nineteenth century, electrotyped) into molds. Clay, wax, plaster, stucco, bronze, brass, lead, zinc, silver, and gold can all be cast into molds.
Mold seams are raised lines, caused by the fine space that exists between the mold sections, which remain on the surface of a piece-molded object. Mold seams are generally removed to hide signs of the sculpture having been mold-made. (p. 63)
A term most commonly used to describe a naturally or artificially induced surface alteration on metal but which also includes coating applied to metal such as drying oils and paint.
A variety of finishes, giving a range of appearances, were used to patinate fifteenth- through nineteenth-century European bronzes. In order to retain the bright, lustrous appearance of a polished or brushed bronze surface, a protective coating of drying oils could be applied, sometimes with resins or pigments added. To achieve a variety of rich golden, to brown, to black surfaces, chemical patinas -mixtures applied to the metal which cause chemical changes - were used. A chemically patinated surface could then be coated with a drying oil and resin lacquer for additional gloss or coloring. A more opaque, paintlike coating was also frequently used, possibly to hide casting blemishes. Protective tinted wax coatings of more recent vintage are found on many Renaissance bronzes; as these coatings alter the appearance of the surface, they may be considered part of the patina. Because many early bronzes have been repatinated, the original appearance of the surface has been lost.
Patina is also used to refer to the natural changes that occur to the surface of nonmetals, for example, the yellowing of ivory with age. (p. 68-69)
A mechanical process used for the reproduction of sculpture.
The name derives from points marked on a MODEL, which are used to transfer measurements to a marble block as it is being carved. Different types of pointing systems were developed for creating same-size, reduced, or enlarged reproductions. In the eighteenth century and earlier, a large wooden frame was placed over the model and over the marble block to provide fixed reference points for measuring horizontal and vertical distances.
The most common nineteenth-century pointing machine consisted of a smaller wooden frame with movable arms. A plaster pointing model was prepared by marking numerous points locations on its surface in pencil. A number of raised reference spots were also set into the plaster to serve as the main locations on which the pointing machine would rest while measurements were being taken. The frame was secured to the model's reference spots and the movable arm or arms positioned so that the exact location of one or more pointing marks was registered. The frame was then secured to the corresponding reference points on the marble, and the movable arm used to indicate the depth to which each location on the marble should be drilled. Once the holes were drilled, the marble remaining between the holes was carved away. In cases where the artist chose not to carve to the full depth of the drilled hole, remnants of the pointing marks can often be seen as concave areas recessed below the finished marble surface.
Pointing allowed the rapid roughing-out of marble sculptures in any desired size. It allowed the artist to freely develop his forms in a more pliable material such as clay or wax, while the casting of the model in plaster and some, or all, of the marble carving could be carried out by skilled technicians and professional stonecutters. (p. 70-71)
A technique for casting metals, which was first used for simple sculpture and utilitarian objects in the Renaissance, grew in popularity in the early eighteenth century, and became the primary method for casting iron and bronze in the nineteenth century.
In sand casting, a piece MOLD is made from a plaster, bronze, wood, terracotta, or wax MODEL using a sand fine enough to record details, yet permeable enough to allow gases to escape. The sections of the piece mold are held together and supported in two iron boxes (called flasks) packed with coarser sand.
A simple sand core can be built up by hand or the piece mold can be completely filled with sand, which is then carved to form the final core shape. An alternative method for forming sand casting cores, which became popular in the nineteenth century, is to fill the piece mold with plaster, which is then carved down to the shape of the final core. A mold taken from the plaster core is then used to cast numerous sand cores. The finished core is held in place with metal core pins or with wires that protrude from the ARMATURE into the surrounding piece mold sections. Channels are cut into the piece mold: gates to allow for the free flow of molten metal and vents to aid the release of air and gases. After the mold sections and core are baked to evaporate water and harden the sand, the flasks are secured tightly together, set on end, and the molten metal is poured into the gates. Once the metal has cooled, the flasks are opened, the sand is knocked away, the core and armature are removed as much as possible, and the surface is CHASED (including the removal of raised mold lines) and PATINATED.
As the technique developed, casting of more elaborate sculptures became possible, although highly complex compositions had to be cast in separate sections and then joined. Sand cast sculpture differs from sculpture made by the LOST WAX process in the "stepped" quality of its interior (a result of the core's being carved rather than modeled) and its overall rough and pebbly interior texture. Because of the efficiency with which the sand absorbs gases released during casting, sand casts generally exhibit less porosity than lost wax casts (see LOST WAX CASTING). (p. 79-80)
1. Lost wax casting process, Bronze with sprues and vents, Copenhagen, Museum of Fine Arts (ph Wikimedia, ESM)
2. Jean-Baptiste Carpeaux, Amélie de Montfort, sketch of standing female, New York, The Metropolitan Museum of Art, 1989.289.2 (ph. www.metmuseum.org, May 13, 2011)