A finished ring came across our QC bench with a 0.2 mm pinhole dead center on the flat top of a signet bezel. It was tiny. But it sat where a customer's eye lands first, and once polished it looked like a dark speck. We pulled it for repair. A different ring had the same size pinhole hidden under the basket where no eye would ever see it; that one passed. Casting pit QC is not about zero pores. It is about knowing which pits matter and where they are acceptable.
What casting pits actually are
A casting pit (pinhole, porosity pit) is a small void left in the metal after solidification. It comes from trapped gas, shrinkage, or investment that did not flow. Most are microscopic. Some are open to the surface and show up as a dark dot under loupe. Closed subsurface pores only appear after polishing. The causes are general; we break them down in casting porosity causes and remedies. The IGI grading framework applies to stones, but the same principle of context matters for metal: location drives severity. A pit on a customer-visible top face is a defect; the same pit hidden under a basket is invisible forever.
Our 10x inspection routine
- First look at the raw casting. Before pickling, hold the piece under a 10x loupe in bright light. Surface pits show as dark spots.
- Map the high-visibility zones. Table tops, outer band faces, pendant fronts and bezel rims are customer-visible. Anything over 0.1 mm there is a candidate for repair.
- Polish-check. After the first polish, re-inspect. Polishing opens subsurface pores, which is why raw-casting inspection is only half the job. This is the same step in final loupe and ultrasonic QC.
- Ultrasonic soak. A 3-minute ultrasonic frees grit from pits; if a pit fills with dark residue after cleaning, it is open and needs filling.
- Repair or reject. Filled pits are refinished; structural pits in load-bearing areas (shank walls, prongs) reject the piece outright.
We inspect in a fixed order so nothing is skipped: outer band first, then bezel rim, then table top, then under the basket, then the inner shank. Each piece gets the same route, and the inspector ticks the zones off on a printed sheet. The full pre-shipment checklist is in jewelry factory QC checklist that cuts returns.
Which pits we reject and which we fill
- Reject: pits on prongs, on shank walls under stress, or larger than 0.3 mm anywhere visible. These weaken the piece.
- Fill and refinish: small surface pits on flat decorative areas, less than 0.15 mm, repaired with a matching alloy fill and re-polished.
- Accept: microscopic pinholes on non-visible areas (under basket, inside shank) that do not open after polishing.
Consistency between inspectors matters, which is why our order-level QC checklist includes reference photos of accepted vs rejected pits so every bench applies the same standard. We also track the reject rate per design; a model that throws 10% pits on the table top gets sent back to the foundry for a re-sprue rather than repaired run after run. Repair work goes to a separate bench: we laser-fill small surface pits with matching alloy, refinish the area, and re-check under loupe so the fill blends. Structural pits on load-bearing walls are never filled, because a filled pit hides a weak section that will open up after a few months of wear. Those pieces are remelted and recast. We do not ship a piece with a filled structural pit on the assumption the customer will never see it; that is how returns start. The QC log on your order lists every repaired pit with a before-and-after photo, so you know exactly what left the bench. We also flag the raw casting inspection zone on the job sheet, so if a pit appears late on a finished piece you can tell whether it was a hidden subsurface pore or a polishing-opened one, and trace it back to the right flask.
FAQ
Are tiny pits normal in cast jewelry?
Yes. Microscopic pinholes are common in investment casting. The standard is that no customer-visible, open pit remains after polishing.
Can a pit be welded shut?
Small surface pits can be laser-welded with matching alloy and refinished. Deep or structural pits cannot; the piece is remade.
Does polishing remove pits?
Polishing can close very shallow pits but often opens subsurface ones. That is why we re-inspect after polishing, not before.
How do I communicate pit tolerance to a factory?
Send a written spec: e.g. "no open pits over 0.1 mm on customer-visible surfaces; no pits on prongs or shank walls." We log that spec on the job card.
Want a factory that logs pit acceptance against your written spec, with before/after photos? Build your QC standard with our custom manufacturing team — we tailor inspection to your brand's tolerance.
The Gemological Institute of America’s gem encyclopedia is an authoritative, widely cited reference on moissanite and diamond quality factors.
