Answer first, and honestly: this page is an authentication guide, not a sourcing guide. A 31mm Cartier Ruban is a small, low-production ladies' watch, and the details that separate a genuine example from a counterfeit sit in the places product photos never reach. Engraving depth on the caseback, the cabochon on the crown, dial print under a loupe, and the movement inside decide the question. The criteria used below are the six that matter in practice: case and caseback finishing, dial and hands, crown and crystal, movement and interior stamping, bracelet or strap hardware, and paperwork with serials and service history.
One rule frames everything else. Cartier finishes watches to a standard that is expensive to copy at scale, and counterfeiters copy what cameras see, not what a jeweler's loupe sees. If you cannot inspect the watch in person or have it opened by a watchmaker, you cannot reach a conclusion.
Case and caseback finishing
Cartier casebacks carry the reference number, the serial number, the metal purity mark, and country-of-origin text. On a genuine case these engravings are cut cleanly, with consistent depth and sharp interior edges.
- What holds up: crisp, evenly spaced engraving; hallmarks appropriate to the metal, such as 750 for 18k gold; correct reference and serial pairing.
- What fails: laser-etched or acid-etched lettering with rounded edges; a reference number that does not correspond to a 31mm case; mismatched font weights between lines.
Run a fingernail across the engraving. Real cuts catch; etching does not.
Dial, hands, and printing
Dial work is where most replicas lose. Under 10x magnification, check the brand signature, the Roman numerals, and any rail-track printing. Genuine printing is dense, matte, and has no bleed into the dial surface.
- What holds up: sharp serifs, even spacing around the numerals, hands with polished bevels and correct proportions for a 31mm case.
- What fails: fuzzy or thick printing, numerals that lean, hands too short or too bright, a dial that reads glossy where it should read matte.
Crown, cabochon, and crystal
The winding crown on a Cartier almost always carries a blue cabochon. Genuine stones are set firmly, show depth of color, and have a polished dome. Imitations use resin or glass that looks flat under light and often spins loosely in the setting.
Movement and interior markings
This is the decisive check and it requires a caseback removal by a qualified watchmaker. Examine the movement finish, the jewel count, and any maker's mark or caliber stamping. Counterfeit movements frequently show unfinished surfaces, misaligned screws, and caliber numbers that do not match the reference.
Bracelet, strap, and clasp
Inspect the clasp stamping, the folding action, and the end-link or lug fit. Genuine hardware closes with a solid single motion and shows the same engraving quality as the case. Loose hinges, sharp edges, and shallow stamps are consistent with counterfeit assembly.
Paperwork, serials, and verification
Papers and boxes are the easiest part of a counterfeit package to fake, so treat them as supporting evidence rather than proof. What carries weight is a serial number that Cartier can confirm, plus a documented service history. Cartier offers authentication and servicing through its own boutiques and service centers, and that is the only answer that ends the argument.
- Photograph the caseback engraving and the crown in raking light.
- Have a watchmaker open the case and photograph the movement.
- Submit the reference and serial to Cartier for confirmation.
- Compare any service records against the watch in hand.
Who this guide is for
Buyers evaluating a secondhand 31mm Cartier Ruban, owners who inherited one without papers, and resellers who need a defensible condition report. If a seller resists an inspection or an independent movement check, that refusal is itself the most useful data point you will get.