I have been making jewellery for 40 years primarily by making wax models and then having those models used to form plaster moulds and then cast in precious metals using the lost wax casting method.
The wax used for modelling purposes comes in various different hardness and can be cut by saws and is normally carved using different shapes of file, scalpels, various shapes of rotary burr or using heated tools to melt the wax. Wax parts can be made and then stuck together to form other structures. Making complex and very often delicate wax models by hand demands a lot of skill and years of practical experience and these are true “one of a kind models”.
Lost Wax Casting
Once a wax model has been carved, the model is sent to a specialist casting company. Initially a branch “feed” called a sproue is added to the model. The model with it’s new sproue is then built onto a wax “tree”. So our model may be one of 50 models built to form the tree structure with all the sproues branching out from a central trunk. This structure is then placed in a stainless steel tube and “Investment” plaster is poured into the tube under a vacuum to remove any air bubbles to form a mould. Once the mould has hardened it is then placed in a kiln and the wax melts and drains out... hence the name Lost Wax method. The mould is now put into a centrifugal vacuum casting machine and molten precious metal is shot into the mould using the centrifuge. After the mould has cooled down and the stainless steel flask removed the plaster is shot blasted away leaving a solid precious metal tree. Our model is cut away from the sproue which has acted as a feed into our model for the molten metal and is sent to me as a rough casting.
3D Printing and Casting
Once a CAD model has been finished and a casting needs to be produced the first thing that needs to be done is to create an STL file for stereolithography. This type of file allows a 3D printer to cut the CAD model into hundreds of 50 micron slices and then print those slices one on top of the other to build a 3D solid model in casting resin. So at this stage we are in the same position we were in with the wax hand made model... a sproue is added, the resin tree built, a mould is formed, is added to a kiln where the casting resin is burnt out and then the precious metal is shot into the flask as before.
Advantages of CAD/3D Printed Models V Hand Carved Models?
CAD modelling allows for extremely accurate placement of stones with each setting being exactly the same distance apart if needs be... this is very difficult to achieve with hand to eye wax modelling. As every part of a CAD model can be measured it is easy to check that all the parts are the correct wall thickness to cast properly and this is much more difficult to do with a handmade model. Once a CAD model has been saved, many variations can be made from that initial file whereas hand wax modelling creates true one off a kind models which due to the casting method are destroyed in the mould making process. If for any reason the casting process fails due to air bubbles in the mix or broken pieces of investment then a new one off would have to be made but with CAD the saved file can be used again.