The short answer
Look at the moon first. On a real Blancpain Quantième Complet, the moon phase sits at 6 o'clock behind a shaped aperture, the moon disc is an actual wheel that creeps forward a fraction each day, and the sky behind the moon is finished, not printed. On most fakes that window is a day and night disc dressed up as a moon phase. It does one full turn every 24 hours. Set it, wait a day, and the moon will be somewhere it should not be. That one test kills most of them.
Why the moon phase is the weak point
A moon phase is a complication. It needs a reduction train that steps a disc once per day so the cycle finishes in roughly 29 and a half days. That is real machinery with real parts count. Printing a blue circle with a face on it and pressing it onto the hour wheel costs almost nothing. So on a fake, the moon phase is usually the cheapest thing on the watch and the easiest thing to catch. I always test it first and only then look at the rest of the dial.
What to check on the disc itself
- The moon. Real discs show a moon with a defined profile, often with a face in relief, finished in polished gold or rhodium. Fakes tend to be a flat printed circle with a cartoon grin.
- The stars. Genuine ones are small, slightly irregular in spacing, and sit inside the blue finish. Fakes often repeat the same star motif or look like a decal.
- The sky. It should be deep, even blue with a finish that matches the quality of the dial around it. Washed out or plasticky is a bad sign.
- The edges. The disc should vanish behind the aperture mask. If you can see the rim of the disc, or a gap at the top of the window, you are looking at a print job.
Set it and watch it move
Use the recessed corrector on the case flank to set the moon phase to a known day. Note where the moon sits. Check again 24 hours later. A genuine example will have moved a small step, roughly one twenty-ninth of the cycle. A fake will have travelled half a turn, snapped to a new position, or returned to the same spot.
While you are there, feel the correctors. On the real thing they are recessed and need a peg wood or a toothpick to press. They also do exactly one job each: day, month, moon phase, date. On a fake, the pushers often click something unrelated, or two of them move the same function.
Dial side tells
A Villeret complete calendar usually gives you the day at 9, the month at 12, a serpentine date hand, and the moon at 6. Under a loupe, printing should be crisp with clean serifs on the wordmark and even spacing. The date hand should be heat-blued steel, thin, and gently curved, not a flat painted strip with a bright blue sheen. Indices should be faceted applied gold.
One hard stop: there should be no lume on a Villeret moon phase. It is a dress watch. If anything on that dial glows in the dark, stop there.
Movement and caseback
With a display back, look for Geneva stripes, blued screws, perlage on the base plate, and a rotor engraving with the correct caliber number in the correct letterform. Replicas usually drop in a generic automatic, decorate it lightly, and etch the rotor shallowly with the wrong font. Also compare the reference and serial engraving on the back with the numbers between the lugs. Mismatched or laser-faint engraving is a flag.
Case, crown, and finish
The Villeret complete calendar case runs around 40mm, in steel or rose gold, with stepped lugs and a mix of polished bevels against brushed flanks. Look at the transition between the two: on a real case it is a crisp line, on a fake it is soft and rounded. The crown should be signed with the JB mark. The sapphire should be clear with no purple or grey haze at an angle.
The price test
Genuine pre-owned Blancpain moon phase complete calendars start in the high four figures for steel and climb quickly from there with metal and condition. A complete calendar with a functioning moon phase for a few hundred dollars does not exist. If the number is too good, the moon phase is a sticker, and everything else about the watch follows from that.
Quick checklist
- Does the moon move a small step per day?
- Is the moon a relief profile or a flat print?
- Are the stars irregular and set inside the blue?
- Does the disc hide behind a shaped aperture mask?
- Is the date hand heat-blued and thin?
- Is there any lume on a Villeret?
- Do the case correctors need a tool to press?
- Does the price reflect a real complete calendar?
Work that list in order on any watch you are considering, and you will usually have your answer before you reach the movement.