You approved the render, signed the sample, and now the order is "in production." For a buyer who has never stood on a casting floor, the gap between that approval and the parcel arriving can feel opaque. Lost-wax casting has not changed its core logic in thousands of years, but the equipment, controls, and failure modes are specific. Understanding the sequence lets you ask better questions and spot which factories cut corners.

1. Pattern making: from CAD to a physical wax

The process starts not with metal but with a wax or resin pattern. For modern shops this usually means 3D-printed castable resin, though hand-carved wax is still used for one-off organic forms. The pattern is a 1:1 model of the finished piece, minus the allowance the caster builds in for shrinkage and post-casting finishing. A pattern that is too small here cannot be fixed later; a pattern that hides undercuts will refuse to release from the mold.

2. Treeing: attaching patterns to a sprue base

Patterns are wax-welded onto a central wax sprue, forming a "tree." The sprue is the channel through which molten metal travels and the path for air to escape. Gating design is where most casting quality problems are born: sprues that are too thin freeze early and create shrink cavities; sprues placed on thin details trap air and leave voids on visible surfaces. A mature caster will gate hidden areas, not the display face, and size the sprue so metal last solidifies at the sprue, not in the ring.

3. Investing: encasing the tree in ceramic

The tree is lowered into a flask and vacuum-mixed investment plaster is poured around it. Under vacuum, trapped air is pulled out; without it, bubbles cling to the wax surface and become rough pits on the casting. The flask then sets for several hours into a rigid ceramic shell. This shell must survive temperatures near the melting point of the alloy you are casting.

4. Burnout: vaporizing the wax out

The flask goes into a kiln and is ramped slowly to around 600-700°C, then held and raised further. The wax melts, drains, and burns away completely, leaving a hollow cavity that exactly mirrors the tree. The burnout schedule matters: too fast and steam blows the shell apart; too cool and residual carbon leaves a "soot" that ruins surface finish and causes metal to ball up instead of flowing.

5. Casting: introducing the molten metal

Preheated flasks are placed under a centrifugal or vacuum casting machine. Metal (recycled plus fresh alloy to maintain karat) is melted with torch or induction and flung or drawn into the hot ceramic cavity. Casting temperature is alloy-specific: sterling silver, 14K/18K gold, and platinum each demand different flask preheats and melt temperatures. Platinum is handled in entirely separate equipment for contamination control.

6. Knockout and cut-off

Once cooled, the investment is broken out by water blast or compressed air. The cast tree looks like a branch with rough metal "fruit." Each piece is cut from the sprue with a saw or disk, and the sprue nub is ground down. At this stage the piece is dull, grainy, and far from finished — it is roughly the shape of the ring but none of the polish.

7. What happens after casting

Casting is only the start. The piece then goes through pickling to remove fire scale, soldering of any attached parts, stone setting, filing, sanding, and a multi-stage polish. Rough castings typically lose 15-25% of their weight to finishing, which is one reason casting weight and finished weight are never the same number on a quote.

What to ask your caster

  • Do you cast in-house or outsource to a trade shop? In-house casting usually means tighter control over gating and burnout.
  • What is the expected casting yield on a design like this? Repeated porosity on a specific piece points to a gating problem, not bad luck.
  • Do you use fresh alloy in a stated ratio, and can you show the karat verification? Recycled-only melts drift in composition.
  • How do you handle porosity in polishing? Small pits can be filled, but large voids are a reject — know the threshold.

Alloy choices at the casting step

The metal you cast with also changes the process. Sterling silver casts at lower temperatures and is tolerant of shorter burnout cycles, which is why silver runs move fast on the floor. 14K and 18K gold need hotter flasks and slower solidification to avoid hot tears. Platinum casting runs on completely separate machines, in a dedicated area, because pickup of iron or silicon from contaminated equipment ruins the alloy. If a factory quotes one price regardless of metal, treat that as a warning: platinum cannot share a line with silver or gold.

Buyers who understand this sequence can read a production update honestly. When a factory says "flask is in burnout," you know the clock has started and that the next decisions — gating corrections, re-casts for porosity — will either protect the margin or eat it. For a deeper look at the downstream work, see our guide to jewelry manufacturing processes.

Sterling silver terminology used in this guide follows the Wikipedia entry on sterling silver.

Frequently Asked Questions

How do I verify a factory before placing a bulk order?

Request a production video, business license, export records and a paid sample run. A factory that accepts a 50-piece test order is usually a real manufacturer.

What payment terms do you offer?

30% T/T deposit with the balance against the bill of lading. This protects both sides on first orders and can move to net terms after a track record.

What is your normal reject rate?

3–5% under 10x loupe inspection for cast and set pieces. Defective units are replaced free in the next shipment.

Where is the factory located?

Wuzhou, Guangxi, China—the core lab-grown and moissanite manufacturing cluster. Shipments go via Guangzhou or Shenzhen ports.