A fake IW329091 gives itself away in the details that are expensive to reproduce: case proportions and finishing, dial printing, lume application, the movement inside, and the engravings on the caseback. Work through those five checkpoints in order, and most counterfeits fail before you ever open the case.
Why the reference number is your first filter
IWC reference numbers are exact. Each one describes a specific combination of case material, dial, strap or bracelet and movement, and the digits are not interchangeable. Before you examine anything else, confirm that IW329091 exists as a reference and that the watch in front of you matches every attribute tied to it. Counterfeit sellers often pair a real reference number with the wrong dial colour, the wrong case metal or the wrong hands, because the number is easy to copy and the full specification is not.
Confirm the specification against the manufacturer's own product records rather than a marketplace listing. If the seller cannot explain why the watch matches that record, treat the number as decoration.
Case, crystal and finish
- Proportions: measure the case diameter and thickness and compare with the published specification. Copies are often a fraction of a millimetre too thick.
- Finishing: genuine cases mix brushed and polished surfaces with crisp, straight transitions. On fakes, the border between the two is soft or wavy.
- Lugs and edges: run a fingernail along the lug edges. A genuine case feels even and lightly broken; a fake is often sharp or rounded off.
- Crystal: check for the anti-reflective coating and look at the crystal edge from the side. A cheap sapphire or mineral substitute shows a different tint and more internal reflection.
- Crown: it should thread smoothly, sit flush and carry clean engraving.
Dial, hands and lume
Dial printing is where most replicas slip. Look at the text under a loupe or a phone macro lens. Genuine printing sits sharp on the surface; counterfeit printing looks bold, uneven in spacing or buried under a visible layer of lacquer. Applied indices should be level, evenly spaced and aligned with the minute track.
Lume is the hardest thing to fake convincingly. Charge the watch under a bright light, then move into a dark room and watch how it fades. A genuine application glows evenly and fades gradually. A counterfeit often glows patchy, with brighter and darker spots where the paste was applied unevenly, and it fades fast.
Check the hands as well. A mechanical movement sweeps in several small steps per second. A single visible tick per second on a watch that should be mechanical settles the question.
Movement and caseback
If you can see the movement, judge the finishing rather than the logos. Stripes, circular graining and polished screws should be consistent, and the rotor engraving should be crisp and correctly spelled. Clone movements often copy the shape while skipping the finishing.
The caseback deserves a close look. Reference and serial numbers should be engraved with even depth and clean edges, not stamped or scratched with a fuzzy outline. Compare the font with other genuine examples of the same reference. Numbers that look too large, too shallow or unevenly spaced are a warning sign.
Papers, provenance and price
- Ask for the original warranty card, booklet and box, and check that the serial number on the card matches the caseback.
- Request a service record or invoice from an authorised service centre if the watch has any age on it.
- Compare the asking price with several current listings for the same reference in similar condition. A price far below the market is a signal, not a bargain.
- Meet at a boutique or a watchmaker if the sale is in person, and ask for written authentication if it is not.
Getting a definitive answer
No checklist replaces a watchmaker with the case open. A qualified technician can confirm the movement, check for swapped parts and verify the case and dial against the reference. Manufacturers and their authorised service partners can also verify a watch during service. If a seller refuses an inspection or a return window, that refusal is the answer. Buying counterfeit goods also carries legal and resale risk in most markets, so a watch that turns out to be fake is rarely a problem you can simply pass on.