Short answer
Fake Portofino moon phase 35 is a search phrase for a replica of the IWC Portofino Automatic Moon Phase. The 35 comes from seller listings. IWC does not sell a 35 mm moon phase Portofino. The genuine watch is the Portofino Automatic Moon Phase 37, reference 4590, at 37 mm. The smaller IWC Portofino Automatic 34 has no moon phase at all.
A listing marked 35 mm is one of three things: a 37 mm replica that measures about 36.5 mm with calipers, a 34 mm Portofino Automatic with a moon phase disc added by the replica maker, or a typo in the listing text.
Genuine reference points
- Case diameter: 37 mm.
- Movement: IWC calibre 35800, automatic, 42-hour power reserve.
- Rate: 28,800 vph, 4 Hz.
- Crystal: sapphire with antireflective coating on both sides.
- Water resistance: 3 bar, 30 m.
- Strap: alligator leather on standard references.
- Moon phase aperture: 6 o'clock.
The 4590 family covers stainless steel, red gold, and diamond-set bezel versions. Dial colors include silver-plated, slate, and blue. Compare a replica to the exact reference photo, because one case takes several dial layouts.
How a real moon phase works
A mechanical moon phase is a disc with two moons. The disc advances one tooth per day. One full turn takes 29 days, 12 hours, 44 minutes. Calibre 35800 runs that 29.53-day cycle. The display drifts about one day from the real moon position after two and a half years unless it is reset.
Most replicas under $150 do not use a 29.53-day disc. They use a 24-hour day and night disc behind a cutout. The moon crosses the aperture once per day. Test it with the crown: wind the hands forward 12 hours. A real moon phase disc turns about 12 degrees. A 24-hour disc moves the moon halfway across the window.
What to measure and check
- Case width. Calipers on a replica listed as 37 mm often read 36.2 to 36.8 mm.
- Moon disc. Genuine discs use a deep blue field with stars and gold or rhodium moons. Cheap discs are flat printed.
- Crystal coating. Double-sided AR gives a blue-purple tint at an angle on both faces.
- Printing. IWC and Schaffhausen sit under the 12 marker. Text on low-cost units is thicker and wider.
- Rotor. Genuine rotors carry decoration and the calibre number.
- Date and aperture position. Confirm both against the reference photo before you judge the dial.
Price ranges
Replica Portofino moon phase 37 watches sell from about $80 to $400. Price tracks the movement, the case finish, and whether the moon disc is a true lunar calendar. Genuine steel 4590 references list for several thousand US dollars. A watch sold as new under $100 with a working moon phase and a leather strap is not running a 29.53-day disc.
Legal note
Replica watches carry the IWC trademark and the Portofino name. US Customs and Border Protection can seize counterfeit shipments. Selling a watch with a copied trademark is infringement.