We cast a lot of models for people who hand carve wax, CAD/CAM/CNC or RP their own designs. Another popular way of making models is to use PMC or Art Clay. The most important part of casting is to make sure you have a model that can be used more than once… hence a metal model is better than a wax model. A finished Metal Model is preferred for mold making as this model will last.  If you want your wax models molded directly, we don’t recommend it as the wax can be broken in the cutting / molding process …also, the wax can be broken later on and the model may be unusable. Wax models are never as perfect as they look. When you cast them you can then see every file mark and problem area. If the model does not clean up perfectly, then it won’t be easy to clean and finish castings from that model. We suggest all wax models to be cast into metal first then cleaned up as best as possible. We prefer all metal models to be cleaned of antique and any other contaminants. If glue has been used on a model, we need to know what kind of glue and where it is. If glue must be used, plumbers epoxy or any epoxy is best. Using No glue at all is recommended.
PMC is one of many model materials we work with and have not had any problems with.  An important part of the model is the thickness of the model on a horizontal plane. It should be no less than 1 mm thick… the longer and wider the model, the thicker it needs to be.   The vertical plane can be thinner in many applications.  Small bezels are a prime example. The side wall specifically at the top of the bezel can be thinner for ease of stone setting.  If it’s a very large bezel, the wall should stay at 1mm.