As the point at which an idea becomes reality, precious metal casting is one of the most important (and exciting) stages in jewellery manufacturing.
Using the lost wax casting process, a CAD model or hand-carved wax is transformed into a physical piece in gold, silver, platinum or palladium.
Precious metal casting takes place in a number of stages, each one affecting the quality of the final casting. We take care of each and every stage.
The history of precious metal jewellery casting
Modern precious metal casting is based on an ancient process, in which molten metal was poured into a mould to form a new shape. Early methods used stone, clay or sand.
When lost wax casting was developed, more precise or intricate shapes could be produced. A mould was formed around a wax model, the wax melted away and metal poured into its place. Although the tools and technology have changed dramatically, the principle remains the same: create a space and fill that space with metal.
Today, precious metal casting is far more controlled. Although every casting house will have its own chosen equipment and methods, the process has been refined over centuries. At JewelCast, we’re constantly reviewing our processes based on new technologies, experience and data, so we can achieve the best possible results for the pieces we cast.
Preparing your design for casting
The casting process begins with a three-dimensional model of the piece you wish to cast. This might be a hand-carved design, a 3D printed model, or a wax taken from an existing mould. This model will later be reproduced exactly in the precious metal of your choice.
Wax is our preferred material for casting. Resins can be cast in some cases, but not every formula is suitable. Some have a high plastic content and do not burn out correctly, which can affect the quality of the casting. This is why any wax or resin sent in for casting will be checked by our experienced casting team before it can go ahead. If we’ve supported you with CAD design or 3D printing, your model will be printed in the correct material for the best possible casting results.
The model is given a sprue, also made of wax. The sprue is essentially a long stalk attached to the piece, which creates a channel through which molten metal will flow. The placement of the sprue is designed for optimal metal fill and to help with casting clean-up – you don’t want your sprue placed over intricate detail or in hard-to-reach areas.
Multiple models are attached to a central core of wax by their sprues, creating what is called a ‘casting tree’. Arranging a tree is a real skill, with each piece positioned to ensure a successful cast for the whole batch.
How is jewellery cast? Investment, burnout and precious metal casting
Once the tree has been prepared, it is placed inside a metal flask and surrounded by investment. Investment is a heat-resistant material a lot like plaster. Hardening around the tree, it captures every detail of the wax or resin models.
The flask then goes into a hot kiln to go through burnout. During this stage, the wax melts away, leaving a cavity inside the investment. This is where the term ‘lost wax casting’ comes from. The wax is lost, and the empty space it leaves behind will be filled with molten precious metal.
These days, we don’t pour molten metal into a mould by hand. Modern jewellery casting uses specialist machines that control precisely how the metal enters the mould. Depending on the casting set-up and metal, this might involve centrifugal force or vacuum pressure, helping the molten metal fill every part of the cavity as completely as possible.
Different metals behave differently during casting, and even different alloys of the same metal can need different handling. We carefully calibrate speed, pressure and temperature to suit the specific metal being cast.
The wrong process can lead to all kinds of problems, from incomplete fills to surface defects to the dreaded porosity. These tiny holes in the metal can affect the appearance, strength and workability of the finished piece, so porosity is one of the issues we work hard to avoid.
With over twenty-five years’ experience in casting, we’ve learned that success comes from the whole process working together.
Quality control after casting jewellery
Once the metal has been cast and cooled, the investment is removed with a high-pressure jet of water, revealing the tree now cast in precious metal.
The individual pieces are then cut from the tree, and the sprues clipped. For particularly delicate pieces we go the extra mile, individually sawing them off the tree to ensure they come off perfectly. This isn’t a usual step in casting, but we think it’s one of those details that makes all the difference. After a quick clean to remove all traces of the investment, every casting goes into quality control. We check that each piece has been cast as expected, from fine detail to surface finish. We know how frustrating it is to work on a piece and then find a problem, so we want to catch any issues now that could affect the next stage of work.
With each stage requiring meticulous attention, casting takes time. It is a lengthy process that takes over 24 hours to complete, which is why we do not offer same-day casting. Casting is the foundation for your pieces, and we won’t compromise quality for speed.
Working with makers, students, designers and retailers, we help bring your jewellery vision to life. You might come to us for casting alone, or after working together on CAD design and 3D printing. Whether we’re helping you create a one-off piece or a whole collection, you’re in safe hands with our casting team.