Once the model is complete, a rubber mould must be made so that a wax replica of the original item can be created for casting.  The mould is made by first laying up the original model with clay slabs.  These clay slabs serve as a smooth, keyed surface around which an outer shell for the rubber mould may be made of plaster, fiberglass or resin. 

When the model has been laid up in clay, the outer shell of the rubbern mould will be made around it.  This outr shell provides firm structural support for the softer rubber that will eventually be on the interior of the mould.

When the mould shell is complete, the clay slabs between the model and the shell will be removed.  The model will then be covered in a separator substance or lubricant and a liquid rubber compound will then be poured into the space surrounding the model within the shell.  When the liquid rubber sets and fully hardens, the mould will be separated along pre-determined seams and the model will be extracted.  The mould is now complete and a wax can now be made.   Below, applying rubber to a mould in process.