Cintrée Curvex

Look at the case from the side, not from above

The compound curvature is the single most reliable check on the brand. A genuine Cintrée Curvex curves along its length and across its width, and the sapphire crystal is curved to match — which is expensive, because a doubly curved sapphire is a difficult component. Counterfeits routinely produce a case curved in one plane with a flat or singly curved crystal. Viewed from directly above, in the photograph a seller supplies, this looks broadly correct; viewed from the side it does not. Insist on a profile view.

The numerals are drawn artwork and copies regularise them

Franck Muller's Art Deco numerals are original artwork with deliberate irregularities — stroke weights that vary between characters, counters of specific shapes, spacing that is optically balanced rather than mechanically even. They exist in no typeface, so a copyist must redraw them by eye from photographs, and redrawn type carries characteristic errors: the irregularities get smoothed out and the result looks tidier than the original. Compare the numerals as a set against a documented example.

Complication claims should be tested functionally

A great deal of Franck Muller's output is complicated, and complications are mechanisms that either work or do not. A perpetual calendar should handle a month end correctly; a chronograph should reset without creep; a tourbillon carriage should rotate. Counterfeits frequently reproduce a complicated-looking dial over a movement that cannot do what the dial claims, and a static tourbillon aperture — or one containing a rotating disc that is not a carriage — is conclusive.

Case and movement numbers should be present and should agree

Franck Muller marks individual case and movement numbers on its watches. That supports a genuine internal-consistency check: the numbers should be present, correctly executed, and consistent with each other and with any documentation. Absent numbers, or numbers whose engraving quality differs from the rest of the case marking, are findings. Note that this establishes internal consistency rather than authenticity on its own — the numbers can be copied, they simply usually are not copied well.