The principles of the process have not changed that much. The clay has been replaced by specially formulated 'investment' powders. The wax is 'burned out' in gas or electric ovens with precise temperature control and metal is melted in high tech induction melting machines.
It is still possible to cast directly from a handmade wax but more often a metal model (also called a 'master' or 'pattern') is made. The model is used to make a rubber mould from which multiple wax copies can be produced. These waxes are then used for casting. The rubber mould can be re-used for future jobs as required. Vulcanised rubber moulds are made by sandwiching a metal model between several sheets of rubber. The 'sandwich' is then place in a heated press which causes the rubber to 'vulcanise' and form a rubber block around the model. The mould is carefully cut open to remove the model leaving a cavity into which wax can be injected through the 'sprue' (also 'feed' or 'gate'). Models that are hollow, very delicate or made from materials with a low melting point will not withstand the vulcanising process. In this case a Room Temperature Vulcanising (RTV) or 'cold cure' mould can be made. Once made the same mould can be used to produce waxes to be cast in all different carats and colours of metal.
It is usual to make a model slightly larger than needed to allow for the 'shrinkage' that occurs during casting and finishing. It is not an exact science, shrinkage is not always uniform especially on pieces that have a mixture of thick and thin parts. Usually an allowance of between three and five percent seems to work well. Castings can be produced in volumes from one to many thousands; our customers range from hobbyists and students to some of the biggest names in the trade. The cost of adding a sprue to a model and making a standard (75 x 50mm) mould is usually under £25.