by Ms Nandita Ray
Today jewelry is crafted using the traditional method of simple tools and skilled fingers to modern tools and hi tech means. The flow of ideas and the wide range of designs offer this choice. Mass production or made to order is the other factor in choosing a particular method of production. Here is an attempt to bring to the reader a comprehensive idea about jewelry manufacturing.
I am sure many marvel at the beauty and workmanship of their favorite piece of jewellery. Many questions might spring to mind, wondering how the delicate design was created or the gem set? What makes the jewellery strong? Who are these artisans who wield their art with such aplomb creating intricate piece de resistance’ with impudence? Making jewellery is definitely not a cake walk. Time, technology and experience have contributed to strengthening the art of jewellery manufacturing. When early man began wearing jewellery fashioned out of stones, bones or any attractive material that caught the eye he hammered, pounded, chiseled and rubbed to get the required shape and size. As man matured and ideas grew, new techniques developed to capture his imagination in a world of gold, gems and glitter. From simple discs to 3D designs were woven with the help of tools and technology. Skill still remains the most important tool and no goldsmith worth his salt and valued for his craftsmanship lacks in this department!
Today jewellery is crafted using the traditional method of simple tools and skilled fingers to modern tools and hi tech means. The flow of ideas and the wide range of designs offer this choice. Mass production or made to order is the other factor in choosing a particular method of production. Here is an attempt to bring to the reader a comprehensive idea about jewellery manufacturing.
Methods used in Jewelry manufacturing
Methods that are typically used to make jewellery from gold and silver and its alloys are Investment Casting, Die casting, cuttle fish casting and hand fabrication. Many jewelers use CAD/CAM to make jewellery. CAD computer aided designs and CAM i.e. computer aided manufacturing to reproduce a model piece of jewellery that can be mass produced. Making jewellery requires knowledge and expertise in gold smithing, stonecutting, engraving, mold making, fabrication, wax carving, lost wax casting, electroplating, forging, and polishing. These are the various steps needed to make jewellery. The first step in making a detailed piece is making of a mold.
Jewellery making begins with a mold. A mold is the exact and perfect replica of the piece to be made, copied either from a design or a piece/object. A mold is shaped around the shape/figure with the help of casting process. The casting process involves a number of steps. There are two methods of casting, investment casting or die casting each with its own advantages.
Investment Casting is also called ‘lost wax casting’ since the wax is removed by heating in a kiln or in an autoclave. It is the earliest metal technique evolved by mankind and has a history of 4,000 years. Believed to have been developed by the Mesopotamians, it remains the most popular process of making gold (metal) jewellery and forms the basis of modern investment casting process. This process involves dipping a mold into a ceramic mix. Sometimes new materials like plastic or polystyrene foam is used instead of wax. This process has a number of steps involved.
- A primary model is made in hard alloy like nickel silver or just silver.
- A rubber model is made by surrounding this primary model, using sheet rubber in a mold frame. It is then vulcanized by placing it in a heated press. On cooling, it is cut with a scalpel into halves or more and removing the primary model.
- This rubber mold is used to make many copies of the primary model on wax.
- Molten wax is then introduced into the mold cavity by using a wax injector. On cooling the wax is removed to get an exact copy of the primary model in wax.
- After the desired number of models has been made the waxes are arranged in a tree all around a central feeder in the casting machine. The central feeder is also called sprue. The tree placed in a metal cylinder called flask.
- A special mixture called investment plaster is mixed with water to form a thick liquid and poured over the tree covering the wax models. Low vacuum removes air bubbles and then this is allowed to cool and harden to form stiff and sturdy molds.
- Then the flask is inverted and placed in a kiln/furnace. The wax is melted by steam or air to remove all the wax. The furnace is set in stages and the maximum temperature reached is 750 degrees centigrade. The melting process takes about 12 to 16 hours. This melting down of the wax is called the ‘lost wax process’.
- The wax is slowly melted and drained out completely and all that is left behind is the investment plaster mold and this will now be used to pour the required molten metal (to be cased) into.
- The casting process begins by putting the flask in a casting machine. The gold metal or its alloy is melted and then cast into the investment mold. Then it is allowed to cool and solidify.
- After it has cooled down completely it is immersed into cold water which breaks off the investment mold, leaving the casts in the tree. The casting are cut off and then made into jewellery pieces which will then be polished into completion.
Two types of casting machines are used the centrifugal casting machine which is the older technique or the modern technique of static vacuum assist machines.
Advantages of investment casting
It is an age old proven method. It allows the jeweler flexibility to create complex designs. The details can be copied perfectly. The control of color is better. The finished product can be highly polished. It results in very fine surface finish. The metallurgical properties are also excellent.
Disadvantages of investment casting
This process can result in porosity. Also the dimensions may not be as accurate as the die struck method. This process can and is used for almost all gold jewellery and remains a favorite with jewelers even after 6,000 years later!
Die struck method
Die struck method is a casting method where the metal to be cast is forced under pressure into a mold which is usually made out of metal. This is a bona fide method of producing complex shapes. The earliest recorded history of die casting by pressure occurred in 1800’s. Using a plunger or compressed air, molten metal is forced into a metallic die and the pressure is maintained until the metal settles and solidifies.
The pressure reaches 25 tons per square inch. The intense pressure causes the atoms in the metal to move closer together and solidify to form dies or molds. Using compressed sheet metal and steel dies mountings are formed with metal parts mechanically stamped out. Each part is matched and fitted into the correct portion of halved die and stamped and shaped. A hydraulic press is used.