I made the silicon moulds with a view to the following process: 3d printed model - wax model - polish wax model - plaster mould - glass model.
Glass takes time and money so I've made prototypes using glass wax. It's delicate and impermanent but it transmits light like cast glass.
I found that the surface of the glass wax can be polished with white spirit. It has to dry off so the silicon moulds are perfect to keep the pieces upright.