A QC bench ships 500 pairs of stud earrings a week. The bench runs a visual check under a lamp, signs off, and ships. Two weeks later, a retailer sends back three pairs with tiny pits visible at 10x and one pair with a loose post. The QC log says passed. The problem is that visual-only QC at arm's length is not a QC process; it is a luck process. Final inspection on jewelry wants two tools: a 10x loupe (or a stereo microscope) and an ultrasonic cleaner. One catches surface defects; the other catches trapped residue and loose stones.

The loupe pass: what to actually look at

At 10x, run the piece under a cool LED lamp and check five zones in order: (1) the setting seats, no daylight between prong and crown, no chip on the stone girdle (see GIA 4Cs finish standards); (2) the soldered joints, no gray grain, no fire-scale, no void at the shank head; (3) the high-polish surfaces, no swirls left from tripoli, no burn marks; (4) the engraving or milgrain, no burr inside the cut; (5) the inner band, no sharp sprue nub, no leftover investment. The IGI grading workflow uses the same 10x pass; a stone that passes a visual check but fails a 10x check is a return ticket.

The ultrasonic pass: what it catches that the loupe misses

Drop the piece in a warm ultrasonic bath with a neutral jewelry cleaner for 3 to 5 minutes, then rinse and dry. This catches three defects the loupe cannot see: (1) trapped investment inside a hollow or filigree, which shows up as a fine dust after the bath; (2) loose stones, a stone that is only tension-held will click or fall out under ultrasonic vibration; (3) leftover polish compound inside engraving or pave, which looks clean on the bench but clouds after a week in the customer's jewelry box. The ultrasonic also doubles as a pre-plating clean, which is why rhodium adhesion depends on it.

What the loupe and ultrasonic do NOT catch

No tool on the bench catches a weak solder joint that will fatigue in six months of wear, or a stone that is correctly set but will loosen after 100 wear-hours. Those are caught by documentation: photo records of every prong at 10x, plus a wear test on a sample piece from the batch. We run a 24-hour tumble test on one sample from every 100-piece batch; if the sample comes out with a loose stone, the whole batch goes back. Our notes on order QC checklist cover the full pass, and what jewelers inspect before shipping ties the visual, ultrasonic, and tumble steps together. Check QC photos before shipment before you sign off; the photo record is the warranty.

Sampling rate and batch sign-off

For a 100-piece batch, we 100% loupe-check every piece, ultrasonic-clean 100%, and pull 5 pieces at random for the 24-hour tumble. If one tumble sample fails, the whole batch is re-checked. We photograph the five tumble samples, attach the images to the work order, and send a one-page QC summary with the shipment. The summary lists batch size, loupe pass rate, ultrasonic findings, and tumble result. We also run a final weight check against the CAD spec; a piece more than 5% under weight usually means a thin wall that the loupe missed, and a piece more than 5% over means excess metal left from a sprue nub. Retailers who receive that summary know in ten seconds whether the batch is theirs to ship or ours to fix.

FAQ: Final QC, loupe, and ultrasonic checks

How long should a piece sit in the ultrasonic?

3 to 5 minutes in warm (40 C) neutral cleaner. Longer does not help and can loosen glue-set stones.

Can I ultrasonic-set pearls or opals?

No. Pearls, opals, emeralds, and turquoise are porous or fractured; wipe by hand and skip the bath.

What magnification do you use for the prong check?

10x loupe or stereo microscope. 20x is overkill for production and slows the bench without adding signal.

Why tumble-test one sample from 100?

Because wear happens over time, not in the bench pass. A 24-hour tumble compresses about 6 months of wear and exposes joints that would fail in the field.

For custom manufactured orders, our QC bench runs the full loupe, ultrasonic, and tumble sample, photographs every batch, and sends a one-page QC summary with the shipment. Send us a CAD, a wax, or a sample; small-batch custom manufacturing starts at 30 pieces, and every batch leaves with its QC record attached. If a batch comes back with a defect, we pull the QC record, identify the step, and re-run the affected step on the whole batch at our cost, not the customer's.

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.