Quick answer
A counterfeit Cartier Tank Louis Cartier is a watch built to look like Cartier's gold Tank while hiding the fact that it is not one. The genuine piece is an 18k gold case on a hand-wound 430 MC movement, sized around 33.7 by 25.5 mm, with a sapphire cabochon crown and dial printing done with a very specific weight of ink. Fakes give themselves away in four places: case thickness and profile, dial print and cabochon, movement, and the engraving and hallmarks on the back. Everything else is detail.
Start with the case profile
The Tank Louis is a slim watch. Counterfeit cases often run a full millimeter or more thicker, because the movement inside needs the room. Look at the watch from the side. The brancards should curve gently and the lugs should flow into them as one piece of metal, not look fused on afterward. Weight matters too. An 18k gold case feels dense in the hand, and gold plating over brass or steel does not.
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The dial is where most fakes slip
Cartier prints the Roman numerals with sharp serifs and consistent stroke width. Under 6x magnification you can see whether the ink sits flat and clean or bleeds at the corners. The hidden Cartier signature worked into one of the numerals, usually the VII, is another checkpoint: on genuine dials it reads as a faint part of the numeral, while on copies it is either missing or drawn too boldly. The cabochon should be a domed synthetic blue spinel that catches light across its whole surface. Flat, milky, or plastic-looking cabochons are a bad sign, and so are painted hands instead of properly blued steel ones.
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Movement
The current Tank Louis runs the 430 MC, a thin hand-wound caliber beating at roughly 21,600 vibrations per hour. Fakes almost always carry a quartz movement or a decorated automatic from a generic factory. If the seconds hand ticks once per second, you are looking at quartz, and no genuine Tank Louis Cartier does that. If the caseback is solid and you cannot see the movement, the sweep rate still tells you a lot.
Caseback, hallmarks, paperwork
Gold purity stamps, Swiss hallmarks, reference and serial engraving, and the "Swiss Made" marking should all be crisp and consistent. Counterfeit engraving tends to be shallow, uneven in depth, or laser-cut so uniformly that it looks printed rather than stamped. Boxes and papers are easy to fake and easy to buy separately, so treat them as supporting evidence, never as proof.
Counterfeit, replica, genuine: three different things
Worth separating before you spend money. Genuine means it came from Cartier. A replica is made and sold openly as a replica. A counterfeit is a replica presented as the real thing, and that is where the legal and ethical line sits. The claim is the problem, not the resemblance.
What I check, in order
- Case thickness and side profile against a known reference.
- Dial print at 6x, plus the hidden signature in the VII.
- Cabochon shape and how it holds light.
- Seconds hand behavior to rule out quartz.
- Caseback engraving depth and hallmark placement.
- Seller story, price, and whether the paperwork matches the watch.
Bottom line
No single tell decides it. Two or three soft signals together usually do. And if a "Tank Louis" shows up at a fraction of gold-case money, assume the metal is not gold until someone proves otherwise.