Short answer
A fake Cartier yellow gold watch normally fails three checks: the caseback carries no 18k or 750 hallmark, the case feels light for its size, and the engraving looks shallow or uneven. Real 18k yellow gold Cartier cases are stamped with the French eagle head or a 750 mark, they weigh far more than steel or plated copies, and the lettering inside the caseback stays sharp under a loupe. If the seller cannot show the hallmark, the weight, and a clear photo of the caseback stamps, treat the watch as a replica and price it that way.
Step by step: verify a yellow gold Cartier
- Weigh the watch on a scale that reads to 0.1 g and compare the result with the listed weight for that reference.
- Read the caseback with a 10x loupe and note whether a 750 mark, an 18k mark, or an eagle head stamp is present.
- Move a small magnet along the case and bracelet, since gold is not magnetic and any pull points to plated steel or base metal.
- Rub the back of a lug on an unglazed ceramic tile, because yellow gold leaves a gold streak while plating leaves a gray line.
- Inspect the bracelet screws and link edges, where thin plating wears through first.
- Ask for the reference number and service papers, then match the number with the brand archive for that model.
Weight and density
An 18k yellow gold case is roughly 15.5 to 16.5 g per cubic centimeter, so a gold Tank or Santos feels dense in the hand for its size. A plated copy over brass or steel lands 30 to 50 percent lighter than the genuine reference. Compare the total weight of head plus bracelet against the factory figure before you accept any claim about gold content.
Hallmarks and engraving
Genuine French gold carries a tiny eagle head in a lozenge, struck deep and clean. Fakes use laser etching that sits on the surface, blurs at the edges, and fades with polishing. The reference and serial numbers on a real Cartier caseback are cut with even spacing and consistent depth. Crooked digits, a missing serial, or a stamp that disappears under a loupe are signs of a copy.
Plating thickness on replicas
Cheap replicas use flash plating of 0.5 to 1 micron and show brass within months. Mid tier copies run 3 to 5 microns, which lasts a few years with light use. Top grade replicas either use thicker 10 micron plating or solid 18k gold, and both cost far more. Ask the seller for the plating thickness in microns and for the base metal under the gold layer.
Movement and dial details
Open the caseback or ask for a movement photo. Genuine Cartier automatics use in-house or high grade Swiss calibers with signed rotors and Geneva stripes. Most fakes hide a basic Japanese or Chinese automatic with an unsigned rotor and rough finishing. On the dial, check the printed Cartier script, the secret signature in the VII numeral, and the alignment of the date window with the crown.
If the watch fails a check
- Walk away when the hallmark is absent and the seller refuses a weight test.
- Request a written statement of gold content and plating thickness for any gold tone piece.
- Budget for re-plating every 18 to 36 months on any plated watch you keep.