When a European accessories brand sent four of its best-selling pendants to a cheaper casting house, the first re-run came back with a 22% rejection rate: cloudy surfaces, visible shrinkage cavities at the bail, and pendants that weighed 8–10% less than spec. The alloy was fine. The problem was the burnout cycle and the lack of vacuum assist. Casting is the step most buyers only see in the finished piece, but it decides roughly a fifth of your margin. This is what a bulk jewelry casting service actually does, and the numbers you should hold it to.
The cost of a bad casting run
Casting failures are not always visible at incoming inspection. Porosity hidden under plating becomes a leak or a rough spot months after sale. Shrinkage at a bail or gallery means the piece fails under normal wear. Industry casting rejection rates for small shops sit around 8–12%; a disciplined foundry runs under 3%.
| Parameter | Small shop typical | Disciplined foundry |
|---|---|---|
| Casting method | Gravity pour | Vacuum / centrifugal assist |
| Burnout cycle | Fixed, ~4 hours | Programmed, 8–10 hours, verified |
| Porosity rate | 8–12% rejected | Under 3% |
| Weight tolerance | ±10% | ±3% |
| Tree density | Packed tight | Sprued for even flow |
How a bulk lost-wax run is scheduled
A production casting batch starts when approved wax patterns (either injected from rubber moulds or 3D-printed) are mounted on a central sprue. A tree of 30–80 pieces is normal for rings and small pendants. The tree is investment-coated in layers of increasing grit, left to dry, then placed in a burnout kiln that ramps slowly to around 700–750°C to vaporise the wax and leave a clean ceramic shell. The hot shell goes straight into the casting machine, where molten alloy is drawn in under vacuum. After solidification the shell is broken off, the pieces are cut from the tree, pickled, and sent to finishing.
The burnout ramp and the temperature hold are where most corners get cut. Rushing the cycle leaves residual carbon that clouds the casting; overheating the shell weakens it and creates finning. A foundry that logs every cycle is a foundry you can reorder from.
Tree design matters just as much. Pieces sprued too close together shade each other from the alloy flow, while a heavy, over-built tree means more grinding and finishing work after the piece comes off. A good casting house balances yield against finishability, and it will show you the tree layout when you ask.
Specs worth asking for
- Vacuum-assist casting for silver and gold — lower porosity, cleaner detail.
- Programmed burnout with recorded ramp curves, not a fixed timer.
- Weight tolerance of ±3% so your gold-costing stays predictable run to run.
- Alloy certification on the batch (925 silver, 10k/14k) with a mill certificate if you sell into the EU/US.
- X-ray or magnifier porosity check on first articles and a sample of the production run.
Matching the service to your volume
Early-stage brand (under 500 pcs/month): a foundry that also does 3D printing and wax injection saves you subcontracting between shops. Expect to pay a small setup fee for the rubber mould. Scaling brand (500–3,000 pcs/month): weight tolerance becomes a real money item. At 14k gold, a ±10% swing on a 5 g ring is a meaningful cost per thousand pieces, so lock ±3%. High-volume program: ask for dedicated trees, batch logging, and a first-article sample sealed before the full run. That protects you when a design is re-tooled six months later.
Frequently Asked Questions
What is the minimum order for bulk casting?
A typical casting MOQ is 50 pieces per design, because the rubber mould and tree setup cost is spread across the run. Reorders on existing moulds can drop to 20 pieces.
How long does a bulk casting run take?
From approved wax to finished castings, expect 7–12 days. Add polishing, setting and plating and a full order lands at 25–35 days total.
Can you cast in 10k and 14k gold, not just silver?
Yes. We cast 925 sterling, 10k and 14k yellow and white gold, and platinum on request. Each alloy uses a slightly different burnout and casting temperature profile.
Why is my casting cloudy or grainy?
Cloudy castings usually trace to residual carbon from a rushed burnout, or overheated alloy. It is a process issue, not an alloy issue, and it should disappear when the cycle is logged and corrected.
Do you provide alloy certificates for export?
Yes. Every batch ships with an alloy spec sheet, and we can provide mill certificates and the paperwork needed for EU/US customs and karat stamping compliance.
Key takeaways
- Vacuum casting plus a logged burnout cycle moves rejection from double digits to under 3%.
- Weight tolerance of ±3% protects your gold costing; ±10% quietly erodes margin at volume.
- Ask for batch logging and sealed first articles before committing to a seasonal program.
Send a CAD file or a sample piece for a casting quote: first-article sample within 10 days, production in 25–35 days. Request a casting capacity review.
Related: OEM casting and polishing · buying guides · wholesale collection.
Sterling silver terminology used in this guide follows the Wikipedia entry on sterling silver.
