Casting metals for utensils, weapons and adornments is believed to have begun around the year 1000 BCE, when humankind learned that it was relatively easy to change certain metals from solid to liquid through the use of heat.
Pure metals however remained too soft to be useful and workable - so to produce greater hardness and improve colour and shine, different alloys were created by melting and mixing together pure metals.
The search for for greater hardness and durability also involved hammering, forging and stamping metal to make them harder still - in fact stamping metal to make it harder was the origin of the minting of coins as valuable objects.
Metal casting is a technique in jewellery making that allows the creation of shapes that would otherwise involve an enormous amount of waste. It can be used to create flowing lines that are relatively easy to make in wax but difficult to reproduce in metal. Metal Casting also allows the creation of identical pieces eg for earrings or identical links for a necklace.
The main method for casting in jewellery making is know as ‘lost wax casting’:
Making a model or ‘pattern’: Models are most commonly carved by hand from jewellers wax which is available in a range of hardnesses and melting points according to the desired goals.
Preparing the mould: For small scale work in a jewellers studio, delft clay is most often used, packed very tightly around the model and within a two-part frame of wood or aluminium. By opening the frame, the model can then be removed easily, leaving a cavity for the metal to fill.
Model placement: a channel, or’ sprue’ is cut into the clay for the molten metal to run down into the cavity. Air vents are added to allow air to escape and ensure good flow of the metal so that it fills the cavity perfectly, taking on the shape and details of the model.
Molten Metal Casting: metal is heated using a combination of gas and oxygen to around 1000 degrees when it becomes molten and can be poured quickly into the mould. As the metal cools, it solidifies. For larger scale commercial casting of multiple objects at a time, the patterns are attached to a central ‘tree’, a rubber mould is made and a vacuum process is used to move the metal throughout the cavity before it cools.
Finishing: when removed from the mould, the sprue is removed and the surface of the cast piece is filed and polished to achieve the desired finish.
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