US Patent 7318466 Lost wax casting method

A method of manufacture of a multilayer ceramic shell mould out of a master pattern includes the steps of dipping the master pattern in a first slip containing ceramic particles and a binder, depositing sand particles to form a contact layer, dipping the master pattern in a second slip containing ceramic particles and a binder, depositing sand particles to form an intermediate layer, dipping the master pattern in at least a third slip containing ceramic particles to form a reinforcing layer. The ceramic particles of the slips includes mullite, alumina, or a mixture of the two, whereas no layer contains any zircon.