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Jewellery Casting Process and its Advantages

05 Jul 2021

Jewellery casting is a process or method in which a wax pattern is made into a jewellery mould and filled with melted precious metal. Once the metal hardens in the desired shape, it is removed from the mould, filed, set with gemstones, and polished. Jewellery casting is also called lost wax casting or lost wax process, because the wax is inevitably “lost” while making the jewellery. The process takes a design to its physical state as the final product.

Jewellery casting has been in existence for centuries, but it is more dynamic with modern technology. It is used in the large-scale manufacture of jewellery. It is necessary to know, gold casting and platinum casting procedures differ. Since platinum melts at much higher temperatures, it needs specialized skills, equipment, and plaster investments.

Here we introduce you to the gold jewellery casting process, its main techniques, and the benefits of casting. Once you know the basics as a jeweller, you can explain to your customers casting jewellery meaning and the advantages of buying wax cast jewellery from you.

Jewellery Casting Process

The five steps in jewellery casting process are as follows: -

1. Wax model
The casting preparation begins with the wax model. Based on the 3-D rendition of the design, a wax model or resin material model is carved or printed to represent the pattern of a finished piece of jewellery. The model is then connected to a wax stem by a sprue to form a tree-like structure to allow gold to flow through the “tree” with minimum turbulence or resistance.

2. Investment
The tree with the wax stem and attached wax models is placed inside a metal flask and filled with plaster slurry to create an “invested” mould. Once filled with the slurry, any air bubbles and pockets are removed by “debubblizing” the flask inside a bell jar with negative atmosphere. Once the plaster or investment material sets, it hardens into the jewellery mould.

3. Burnout
The hardened invested mould or flask is placed in a specialized kiln to melt away the wax model at temperatures around 1600° F for 12-16 hours. A well-burned flask has no remaining residue of wax or resin, only a hollow impression or cavity left by the tree in the final invested mould.

4. Melting and Casting
The next step is to pour the gold or molten metal into the hollow cavity of the wax-free mould. Various techniques such as centrifugal casting, vacuum-assisted casting, or pressure casting (explained below in detail) are used to ensure the gold flows evenly into the mould. The gold melts at temperatures from 1,617° F to 2,006° F, depending on the alloy used for varying colour and hardness.

5. Divesting
Divesting is the last step in the jewellery casting process. At this stage, the mould is put into a bucket of cold water to destroy the investment form. Any remaining plaster is chipped away, leaving behind a tree containing models as branches. The models are then cut free from the sprue. The gold pieces of jewellery are now the exact replica of the initial wax pattern. While the spruces are recycled, the jewellery is cleaned, set, buffed, and polished.

Lost wax techniques for wax cast jewellery
While there are several techniques in casting like - sand casting, die casting, low-pressure casting, squeezing die casting, there are two main techniques for wax cast jewellery. They are: -
i. Centrifugal Casting Jewellery
Centrifugal jewellery casting machines use the weight of the metal and force of a centrifuge to create the inertia necessary to fill gold into the mould. After burnout, the flask is placed on a rotating arm in direct alignment with the crucible. High-frequency induction or a torch heats the crucible holding the metal. When the metal is at a critical temperature, the arm is released, forcing (by centrifugal force) the melted gold into the mould. The high velocity imposed on the metal fills the flask before it spins to rest.
Centrifugal casting machine also casts high-temperature metals such as palladium, platinum, where the melting temperature reaches up to 4700° F.

ii. Vacuum Casting Jewellery
The vacuum jewellery casting machines use a vacuum to suck the molten metal into the mould. The principal behind vacuum casting is that the molten gold has to be sent with enough force into a flask to enable it to funnel through detailed cavities before cooling.
The vacuum casting machine has two chambers, the upper and lower chambers. Melting of high-temperature metals takes place in the upper section. The hardened investment flask loaded lower in a sleeve sucks molten metal into the investment as it is being poured or released.

Advantages of wax cast jewellery
Technology in jewellery manufacturing has improved the lost wax casting process. It is not only a reliable and easy way to create jewellery but also the most widely used. The main benefits of casting jewellery are:-

1. View 3-D Form
With a wax model prepared for casting, you can see the design in a three-dimensional form which is usually more realistic than a hand-drawn sketch.

2. Continued accuracy
Since casting involves making a mould to create the master, every piece will be identical to the design of your model. Unlike handmade jewellery, casting ensures accuracy in replicating the original.

3. Greater level of durability
Most cast pieces reduce the soldering points that may weaken the jewellery. For example, prongs are cast as a part of the overall piece and not soldered later around the gem to make it more durable in the long run.

4. Highly flexible
Today computer technology can turn your sketch into a mould. That mould is used in the lost wax casting process. The mould provides flexibility to create and bring to life the most intricately designed piece of jewellery.

5. Faster production
Investment castings are used in jewellery manufacturing because they cut down on labour and improve lead times. The cast jewellery requires less time to finish making casting jewellery designs more affordable.

6. Cost effective
Casting the jewellery piece is cheaper than producing the jewellery by hand as it is less time-consuming and labour intensive. Casting is perfect for mass produced affordable jewellery.

7. Easy to duplicate
Casting can produce 100s of duplicate pieces—whether it is an heirloom design or your favourite design. It even helps to duplicate the wedding ring fit to sit perfectly alongside the engagement ring.

Jewellers find wax casting very useful for all the above reasons. With the growing demand for jewellery, casting is the most preferred method of manufacturing jewellery. While gold casting jewellery designs continue to sell, there will always be a demand for exclusive handmade fine jewellery but at a price.

Rukshana is a freelance content and communication strategist based out of Mumbai, India. She mingles her expertise in PR with comprehensive domain knowledge and creative writing skills to assist and propagate business, worldwide. Being a quick learner, she utilizes her diversified digital expertise to provide copywriting and content writing services to create highly profitable brands, products, and services.