Nepalese images and ritual and domestic objects are either cast by pouring molten metal into a prepared mold or hammered out of sheet metal.Casting is done by the ” lost wax ” (cire perdue) method,known in Newari as thajya. In this process a wax model is encased in clay then melted out “lost ” tobe replaced bhy molten metal. After the metl hardens the clay mold is broken away revealing a metal replica of the wax model. A solid wax model produces a solid casting; a hollow wax model with a clay core produces a hollow cast. For reasons of economy and ease in handling, usually only small images and objects are solid cast. All cast images require hand finishing by various processes. Wax models may be one of a kind or replicas.Replicas are made by pressing a warmed harder wax around and original model, of wax,metal,or other material. When the hard wax is removed it becomes a mold into which soft wax is pressed to replicate the original.Today much of the metal used by Nepalese craftsmen is imported but traditionally copper was readily available in Nepal and in ancient times was an improtant export. Thus, older cast images tend to be of copper though conventionally they are referred to as ” bronze ” , a mixture of copper and tin. The use of brass in casting is a recent phenomenon. Because if its relative malleability, sheet copper is the metal of choice for repousse work although brass, silver,and gold are also used. Typically, images whether cast or hammered are ” fire gilt”. From about the ninth century images were increasingly inlaid with precious and semi precious stones. The use of paint and “cold gold ” ( gold leaf applied without heat ) is confined to works made by Tibetans or by the Newars from the Tibet trade.
LOST WAX METHOD OF CASTING
The first step in making a cast metal image in the lost wax process, called thajya in Newari language , is sculpting the image in the wax that will hence be “lost”. The wax mixture is prepared by melting together beeswax, vegetable oil,
and resin from the sal tree, a tropical hardwood. After the wax hardens, lumps of it are warmed and pounded into thin, flat sheets. The wax sheet is further warmed over a charcoal brazier and the artisan begins to gently mold the image with the tips of his fingers. He first shapes the rough contours of the gace and neck and then sculpts the facial features.
The excess wax of the sheet is cut away with a thin, heated steel blade, leaving just the contour of the face and neck, which are then sculpted with a spatula made of buffalo horn, called a silayku in Newari. Using the different shaped ends of this versatile tool the artist further refines the facial features.
The front and back halves of the Buddha head are produced from the separate sheets of wax, allowing the artist to also manipulate the wax from behind. Then the halves are joined, the head covered with small beads of wax which will be refined to represent hair, and the face completed. Here the head is still in halves to allow the inside to be seen.
The head of an image of the Buddha is covered with small beads of wax representing short curls. This is a tedious process because for each curl a precise amount has to be assessed and pinched from a soft piece of wax. It is rolled between the thumb and forefinger, heated over a brazier and attached by pressing it to the head. To further complicate the process the beads in each row change in size depending where they are placed on the head, and then must be further refined by hand using the silayku tool.
To join the halves of the head their edges are heated over a brazier,called a milayca in Newari, and pressed together. A long thin bamboo stick with one end wrapped in cloth,called a sikathica in Newari is dipped into a small pot of liquid was. The liquid wax is dropped onto the unfinished seam which is worked smooth with the silayku tool.
In a bust such as this example, the head,ears and shoulders are always made separately and joined together. With a full body sculpture, the torso, arms, hands, legs, feet and pedestal would also be done in halves, joined and finally all assembled.Seams are completely smoothed out with the buffalo horn spatula. Final adjustments to the image are made by adding and shaping thin layers of molten wax or scraping it off with various sized and shaped knives.
The last step in the wax modelling process of this bust is to attach wax channels to connect chin to chest and ears to shoulders, These channels help distribute the molten metal evenly throughout the mold during the process of casting. Finally the artist carefully goes over the wax image to make sure that no excess wax is present and that the surfaces are smooth.Refinements can be done at this stage by adding soft wax or by cutting away wax with thin steel blades. The completed wax image is what will be “lost” and replaced by molten metal and must therefore be perfect in all its details.
The clay mold to surround the wax is made in four stages. First the wax model is dipped in a fine sieved mixture of clay,cowdung,and water. If the image is to be hollow the mold is also coated inside and requires a clay core.The mold is dried in the shade,dipped in a second layer of the same clay mixture and dried again.Third and fourth clay layers with increasingly higher proportions of cowdung and added rice husk,are applied by hand and dried in the sun. For hollow-cast images, iron nails are driven through all exterior clay layers,the wax model, and into the clay core.The nails keeo the core from displacing when the wax is removed and the molten metal added.
The cowdung has an adhesive quality that ensures proper binding of the clay mixture to the wax. It also regulates the temperature its nitrogen element keeps the mold at the high temperature required for casting and its porosity allows the heat of the molten metal to escape so that the metal can solidify rapidly. When the mold is complete,its bottom layer is scraped away to just expose the wax and waxen channels. Pouring spouts are attached and mud coated. On the casting day, the clay mold is heated and drained of the wax which is not actually lost but collected and saved for future work.
The empty molds and metal – laden crucibles are stacked in separate kilns and fired for several hours. With well honed intuition the masteer assesses when they have reached the right temperatures.The heated molds are removed with 4 foot metal tongs and placed in position to receive the molten metal. With dramatic timing the master rapidly fills each mold with the exact quantity of molten metal needed whhile an assistant throws resin into it to prevent the metal from oxidizing as it cools. To complete the cooling , the metal filled mold is immersed in water, then removed and broken open to reveal the image.
After a rudimentary cleaning , the rough cast image, in this case of copper, is taken to another crafts man for finishing. With special scrapers he removes any residue of the blackened mold and soaks the image in sulfuric acid to complete the cleaning process.The excess metal of the pouring channels is removed with hammers. chisels and dies. Then the entire surface is poured with hammer and die in a cold forge process to condense and harden the metal. This process is generally done by an apprentice who has been tught the process by the master.
The smoothing of the surface is begun with files and sandpaper usually by an apprentice. The master then uses various shaped dies and hammers of different weights to refine the details as illustrated on the right side of the image. The process is called chasing.The finest tools are used to finish ornaments such as the earrings and to engrave delicate textile patterns like those on the folds of the robe over the lert shoulder.if an image is to be gilded a goldsmith does it by a bprocess called fire – or mercury gilding.
The process of gilding is a lenghty,complex and dangerous one. Highly toxic mercury is first combined with ground gold foil to make it dhere to the metal but then driven off by heating to leave only the gold.By various processes the gilded surface is then burnished and polished to achieve a rich golden color. As an ultimate step it may be immersed in a red dye obtained from tree bark which prodeces a warm reddish glow , a finish particularly appreciated in Tibet.
Source : Patan Museum Guide Book