Investment casting is done by creating a mold of the original object. This can be done using a variety of methods, the most common method is lost wax process. In the lost wax process a wax model of the part is created.
The wax model is then covered in a ceramic material. This ceramic material forms a shell around the wax model and hardens in a high temperature oven. The wax model is melted and drained out of the shell, leaving a negative impression of the wax shape inside the shell.
Molten metal is then poured into the shell filling the cavity. After the metal has cooled, the shell can be broken away, leaving behind the part made from the desired alloy.