Comprehensive Study Notes on Sculpture Materials and Techniques
Properties of Clay and Firing Techniques
Clay is considered the most accessible and simplest material for sculpture, widely utilized in modeling, maquette construction, and the creation of full-scale sculptures. To prepare sculpting clay, one requires finely sifted soft clay and water. A specific additive used to prevent the clay from cracking is the Looie plant, which is a type of marshland plant. The amount of kneading is of critical importance; if the clay lacks sufficient water, it becomes excessively dry and will crack during manipulation. Conversely, an excess of water results in high stickiness, which creates functional difficulties. A standard test for ideal consistency involves pressing a piece of clay between the thumb and index finger; it should neither crack nor stick to the skin.
To prevent prepared clay from drying when not in immediate use, it must be thoroughly covered with a plastic wrap. If the work is interrupted for a long duration, the surface of the clay should be moistened with water before it is sealed in plastic. Regarding the firing of clay to produce pottery (ceramics), the piece must not possess excessive thickness. For instance, a solid volume of clay cannot be fired effectively; thus, artists typically utilize various techniques to create hollow volumes. The optimal thickness for successful firing is approximately . Furthermore, the piece must dry under specific controlled conditions to ensure it does not crack or eventually break.
Unolit and Foam: Characteristics and Safety
Unolit (Polystyrene) is a lightweight chemical substance primarily used in packaging, insulation, and maquette making. Its primary advantages in sculpture and maquette construction include its extreme lightness and the ease with which it can be cut. Cutting can be performed using a cutter, a soldering iron, or specialized Unolit cutting machines. These specialized machines are often constructed by artists themselves and consist of a wire that heats up significantly due to the passage of electrical current, reaching a temperature suitable for slicing through the material.
There are significant safety concerns regarding these materials. The gas produced from burning Unolit is highly toxic and harmful. Additionally, when working with fiberglass resin, the use of a mask is mandatory. In molding applications, Unolit is an excellent material for creating flat surfaces and is frequently used for graphic forms such as logos (Aram), letters, and various scripts. Foam is a related chemical substance in the Unolit family, available in the market as thin sheets or blocks for maquette making. Foam sheets are easily cut with a cutter and can be bonded using water-based adhesives like wood glue. It is important to note that thinner-based glues (solvent-based) will dissolve foam.
Patina: The Chemical Art of Surface Finishing
Patina refers to a specific color, often associated with a bronze finish. It is fundamentally a chemical process applied to metal by an artist or industrialist using chemical substances to alter the surface color. When a bronze sculpture is removed from its mold, the object typically lacks an aesthetically pleasing or acceptable color. The process involves removing excess metal, performing surface finishing (paying), and sealing any potential mold seams. The bronze surface is then treated according to the artist's preference.
This is not a standard painting process; rather, the color result from the reaction of various acids and elements on the bronze surface. Artists can achieve a variety of colors ranging from rust green to brown, olive, and smoky brown. Over time, as hands touch and rub against the raised points of the sculpture, the patina layer wears away, revealing the original metal color beneath, which often enhances the aesthetic beauty of the sculpture.
Silicone and Silicone Adhesive in Molding
Silicone adhesive, commonly known as aquarium glue, belongs to the silicone family but differs in that it hardens upon exposure to air, whereas industrial silicones require a hardener (dryer) to solidify. Silicone adhesive is suitable for creating semi-professional molds. Professional silicone is a viscous liquid available in various colors that transforms into an elastic state a few hours after being mixed with a drying agent. It is extensively used in industrial mold-making, artistic molding, and plasterwork. Some varieties have a paste-like consistency and are very sticky, usually applied to the work by hand.
Different types of silicone are specialized for different tasks: some are for reproducing plaster and wax sculptures, some for polyester and cement, and others for casting alloys with low melting points, such as lead. While silicone itself is non-toxic, the hardening agent can cause skin irritation. There are two primary methods for silicone molding:
Layering Method: This involves mixing 100 parts silicone with 5 parts drying agent. The mixture is applied to the model using a wooden spatula. After waiting several hours for the layer to dry, subsequent layers are added until the mold thickness reaches at least . For added strength, pieces of curtain mesh (tulle) can be embedded between layers.
"Hovzeh" (Pool or Basin) Method: The figure is laid on a board, and the area around it is filled halfway with modeling clay. A sturdy cardboard strip is placed around it, with ends glued and seams taped to prevent leakage. Silicone is then poured in until the model is submerged, ensuring the silicone level is higher than the highest point of the figure. Once it becomes elastic, the model and its silicone casing are flipped. The edges are greased with Vaseline, the cardboard strip is reapplied, and a second batch of silicone and dryer is poured to submerge the remaining half, again reaching a level above the highest point.
Plaster Characteristics and "Kushteh" Plaster
Plaster (Gypsum) must be combined with water for use. It is stored as a powder in dry locations to prevent any moisture from reaching it. Plaster hardens through a specific process after mixing with water. If the mixture is stirred excessively during the setting period, it may fail to set properly; this resulting substance is referred to as "Kushteh" (dead) plaster, which is specifically used in ornamental plasterwork (Gach-bori).
Techniques for Face and Hand Casting with Plaster Bandages
Molding faces using plaster bandages is a traditional technique often used for creating death masks of famous individuals, such as Beethoven, Bach, Vivaldi, and Master Saba in Iran. The process is historically associated with post-mortem casting because the subject cannot breathe during the process. To create a face mask, the entire face must first be covered with a layer of solid grease, such as Vitamin A or Vaseline, with special care taken on areas covered in hair like eyebrows. Wet plaster bandages are then carefully layered over the face.
Once the bandages are in place, a layer of plaster approximately thick is poured over the bandages to ensure the mold does not deform. After a few minutes, once the plaster has set, the individual moves their facial muscles to separate the mold from the skin. The interior of the resulting mold is greased, and fresh plaster is poured inside. The best time to carefully destroy the outer bandage mold and extract the finished model is immediately after the poured plaster has set. Hand casting follows similar steps, though the palm of the hand does not require greasing.
Surface Finishing and Metallic Simulation of Plaster Sculpture
To make a plaster relief sculpture appear metallic, the surface is first coated with a layer of matte plastic paint (which dries quickly) or matte oil paint (which takes longer). Finally, metallic powder (Aklyle) is mixed with a small amount of varnish (Roghan-e-Jala) and applied controlledly with a brush to the raised portions of the work. Specific color combinations allow for different metal simulations:
Bronze Effect: A base mixture of Brown + Green + White, followed by Gold metallic powder.
Copper Effect: A base mixture of Green + a small amount of Brown + White, followed by Copper metallic powder.
Tin, Lead, or Cast Iron Effect: A base mixture of Black + a small amount of White, followed by Silver metallic powder.