About John: John is a Syzjewelry jeweler and business owner with 13 years of jewelry-design experience. This guide shares what happens between the wax model and the casting, and the one mistake I watch for.
The rubber mould itself moves 2-4%, and the casting allowance runs 0.5-1.0% on small pieces and 1.0-2.0% on large ones.
The wax is also where the gold weight starts. The wax weight is the starting point for working out how much metal the casting needs.
The numbers I work to
- Rubber mould movement: 2-4%.
- Casting allowance, small pieces: 0.5-1.0%.
- Casting allowance, large pieces: 1.0-2.0%.
What goes wrong
Wax a little too hot, or a mould that is badly vented, leaves a bubble. That bubble becomes porosity in the metal, and it can sit directly under the setting, where nobody sees it.
Questions worth asking
- How is the mould vented?
- What temperature is the wax injected at?
- Is the wax checked before it goes to casting?
Using this on a wax page
The listings on this page are ring waxes for lost-wax casting, so the mould and casting allowances above are the numbers to keep in mind when you cast from them.
Figures are ranges from my own bench notes. Actual practice follows each workshop's process card, order requirements and the current standard.