Casting is a process which has been used in various forms over the last 5,000 years. It is argued that the first true metalworking skill was that of casting (investment or lost-wax casting). Cast silver holds a great appeal due to its fine quality and superior gauge of silver. Cast items are handmade, often in two halves, resulting in fine and delicate detail. Casting was the method of choice for many renowned silversmiths such as Paul Storr and Paul de Lamerie.
There are different types of casting used for different types of materials and metal. We are interested in those used to form cast silver. Silver has considerable strength and a low melting point to which makes it an ideal metal to be cast without difficulty. Here we will be looking into the technical background of the process that is casting.
In its simplest form casting silver is when liquid metal is poured into a mould and is left to set until it hardens. The liquid once set takes on the form of the shaped mould. If you think about water being poured into an ice tray and then left to set; this is how casting works. The disadvantage of this is that objects were flat on one side, to get a full 2D object two halves of a mould are made symmetrically and locked together. Interestingly, due to the mould being closed ventilation holes are placed to allow the metal to set and gases to escape. Due to this sprues are left behind which have to be cleaned off the finished product produced.
Early Types of Mouldings
In the very early days stone was used as a mould, sand moulds came into existence in the sixteenth century. In this instance the object which was to be cast was compacted into the sand to make an impression of it. Another type of casting which was developed was known as slush-casting. Slush casting was created to make hollow objects which saved on metal and produced lighter objects; this process is only suitable for certain types of metals. When the molten metal hits the cold walls of the mould it hardens quickly. A core is built in the construction of this type of mould which holds the still-molten metal in the core which is then poured out.
Investment or Lost-Wax Casting
Since the fourth millennium BC this type of casting has been the most used casting process. With this method…
- A wax model is crafted of the object to be cast, the core of which is changed depending on if the finished piece is to be hollow or solid.
- The model is then fitted with the all-important ventilation vents using wax sprues.
- The model is invested (covered with plaster or clay) and left to harden.
- Once set the clay/plaster is heated gently or baked. The heat causes the wax to melt which drains from the mould and is replaced by the molten metal.
- Once cooled the mould is then removed to reveal the cast piece. If a piece is to be mass produced a master mould is kept to make future moulds; which in today’s modern age is usually made from silicone-rubber but in the past it would have been lead or plaster.
- The finishing process of casting is done after the piece has been taken out of the mould. This is known as the cleaning up process. This is when all dirt, scales, the sprues caused from ventilation holes and core supports are removed.
- Any sharpening of the piece is done along with polishing.
Although the modern age has introduced heavy machinery to help with mass production of cast silver, the basic forming techniques of casting are still to this day done by hand. I’m sure you can agree after reading this that casting is certainly a craft and can produce such beautiful pieces.
Take these magnificent, fine impressive pair of antique George IV English cast sterling silver candlesticks for example. These cast sterling silver candlesticks are the finest gauge and examples of their type you could hope to acquire; the most magnificent pair of this type Andrew Campbell has had the pleasure to include within his inventory.