Metal Processes

Metal can be worked in many different ways. Some processes are very delicate and have to be done by hand, taking a lot of time. Others can be done very fast and mechanically, which is why metals are good for mass production.

The main processes are:

CASTING, when the metal is heated until it is liquid. It can then be poured into different shapes, or moulds. For example the Kneeling Woman Bathing was made using the Lost Wax Process:

 

 

 

 

1) The sculptor made a model ('modello') of clay.

2) The sculptor covered the original model with plaster to create a plaster mould of the work. The original work needed to be removed. This often destroyed the original sculpture

3) Molten wax was poured into the void left by the original model. The wax was swished round to give an even coating on the inside of the plaster mould.

4) The wax figure was removed from the mould and ‘dressed’ to remove any imperfections in the appearance of the sculpture.

 

5) The wax mould was coated in a fire-clay or ceramic shell to create another mould. It was important that this mould had a number of holes and channels called 'cores' built into the mould. This allowed the wax to melt out and air to escape when the bronze was poured in.

6) The mould with the wax model in the middle was placed into a kiln and heated. The heat hardened the outer shell and caused the wax to melt and run out of the cores. This left a negative imprint of the model inside.

7) Once the hardened outer shell had cooled down it was tested to make sure there were no leaks.

8) Molten bronze was poured into the shell and filled the void left by the wax. It was then left to cool down and harden.

9) Once the bronze had hardened the outer shell encasing the bronze figure was shattered to reveal the rough, bronze figure. The sculptor chipped away the cores from the figure and polished the rough surface.

10) The sculpture was then finished by colouring it with a coating called ‘patina'.

ROLLING, when lumps of metal are squeezed between heavy rollers to make flat sheets that can then be made into other things.

STAMPING, using a heavy weight to force a shape or pattern into a lump or sheet of metal. Look at the stamp above. It was used to create the image on the token next to it.

HAMMERING, either with large hammers for construction or small ones for decoration when the metal is hot and soft. This can also be called RAISING, EMBOSSING or CHASING.

ENGRAVING, when patterns or words can be cut into the surface of the metal using fine cutting tools.

One of the advantages of metals is that their surfaces can be decorated with delicate patterns, or by a technique called PATINATION. This is when a natural change in the surface appearance, brought about by the chemical reaction of the metal with the air over time, is encouraged. A good example is the bronze ritual vessel, which was prized for its green colour.