Answer first

A replica Portofino moon phase 35 is a copy of the IWC Portofino Automatic Moon Phase sold with a 35 mm case. The original reference, IW4590 Portofino Automatic Moon Phase 37, measures 37 mm. A 35 mm listing points to a smaller clone case, not the IWC case. Ask for a caliper photo before you pay.

What the number 35 means

IWC sizes the Portofino line by case diameter: 34, 37, 40, 42. No current Portofino moon phase uses a 35 mm case. A listing at 35 mm points to a generic case sold under the Portofino name, a 34 mm copy described with a rounded number, or a listing error. Lug width and strap fit track the case, so parts from a 37 mm watch do not fit a 35 mm copy.

Genuine specs to compare

Case: 37 mm stainless steel. Water resistance: 30 m. Crystal: sapphire, antireflective on both faces. Movement: IWC calibre 35800, automatic, 42 hours of power reserve. Moon phase: IWC rates the display to deviate by one day in 122 years. Date: window at 3 o'clock. Dial: moon aperture, applied indices, leaf hands.

Movement grades in copies

Quartz copies use a printed disc that turns once per 24 hours. That wheel is a day and night indicator, not a moon phase. Mid grade copies use an Asian automatic from the 2813 or 8215 family with a bolt-on module. Top grade copies use a modified 2892 or 9015 with a 59-tooth disc. A 59-tooth disc advances one tooth per day and covers two lunations in 59 days.

Moon phase facts

A lunar month runs 29 days, 12 hours, 44 minutes. A correct disc tracks that figure. A 24-hour wheel repeats the same position at the same hour each day. Test: set the disc to a known new moon date. Check it after seven days. A correct disc sits near first quarter at that point.

Checks before buying

  • Case diameter photo with a caliper or ruler.
  • Movement name from the seller. No name points to quartz or a day and night disc.
  • Lug width in mm, so a strap can be ordered.
  • High zoom photo of the moon aperture. Look for a clean stamped window edge.
  • Crystal material: sapphire or mineral.
  • Water resistance claim. Treat any copy as splash resistant, not water resistant.

Legal note

Counterfeit watches are illegal to sell in the United States. CBP can seize shipments at the border. The importer can face civil penalties. Personal use carries less legal exposure than resale, but the goods remain subject to seizure.