What is the correct process to make a correct resin casting for jewelry?
Factually, the correct process is to heat up the mold hot enough to evaporate the positive. 

In investment casting the process to remove the wax or plastic positive is called the "Dewax" and "Burnout preheating".

The answer to your question depends on the material you use to generate a negative mold of the positive product. E.g. many silicate based materials require up to about 1100&nbsp;&deg;C to fully burnout all residue before pouring in the liquid metal.