Short answer
A fake Patek Philippe 7118 blue dial is a replica built to imitate the steel Nautilus 35.2 mm reference, its blue relief dial, the integrated bracelet, and the caliber 324 S C inside. Most replicas get the footprint close and then fail on four points: the dial relief and color shift, the bevels on the bezel and bracelet links, the finish of the date aperture, and the movement visible through the sapphire case back. No fake matches a genuine example in hand, and selling one as real is fraud.
Prerequisites
- Digital calipers accurate to 0.01 mm
- 10x jeweler's loupe
- Raking light source or a phone flashlight
- Reference photos from Patek Philippe's own product page
- Lint-free gloves and a soft cloth
Step-by-step checks
- Measure the case across the bezel from 9 to 3 o'clock and compare with the 35.2 mm spec, since replicas often run 0.3 mm to 0.8 mm wide or short.
- Set the watch under raking light and tilt it through a full arc to watch the blue shift from deep navy to steel blue on a genuine dial.
- Inspect the applied hour markers with the loupe for polished facets, sharp edges, and lume applied to a level plane.
- Turn to the date aperture and study the frame for a polished inner edge and a flat date disc.
- Run a fingernail along the case flank and the bracelet link bevels to feel the transition from brushed to polished surfaces.
- Open the clasp and read the engraving depth and letterform spacing.
- Flip the watch and look through the sapphire case back at the rotor, bridges, and screws.
- Weigh the head and bracelet on a gram scale and compare with a known reference weight for the reference.
- Read the serial and reference engraving between the lugs and compare the font and depth with archive photos.
What the checks reveal
Dial work is where replicas lose first. Genuine horizontal relief lines on the 7118 dial stay crisp under magnification and hold their color as the angle changes. Fakes show flat pigment, an orange peel surface, or a purple cast, and the marker settings sit too high or carry excess adhesive.
Case and bracelet finishing separate the next tier. Real Nautilus cases carry mirror polished bevels that meet brushed flats along a hard line. Replicas round that line off or polish over it, and the link edges feel soft against a fingernail.
The case back settles the question. A genuine caliber 324 S C shows Geneva stripes, polished bevels on the bridges, and a gold rotor with sharp engraving. Fakes show printed plates, plastic movement rings, or a rotor with shallow laser text. If the movement number does not match the case serial in Patek's archive, the watch is not genuine, no matter how the dial reads in photos.
When in doubt
Take the watch to an authorized Patek Philippe retailer or a watchmaker with brand training and request a written assessment. Counterfeit sales are illegal in the United States, and a purchase without papers, service history, or an authentication report carries the same risk as buying any other unverified luxury item.