A fake Jaeger-LeCoultre Master in gold fails four checks: gold hallmarks, movement, caseback engraving, and crown. Real Master Control and Master Ultra Thin cases in 18k gold carry Swiss precious metal marks, a six or seven digit serial, and an in-house caliber with Geneva stripes. Gold-plated fakes carry none of these. Check the caseback first, then the movement.

Gold Hallmarks

Swiss law requires hallmarks on precious metal cases. An 18k JLC case shows "750" or "18K", the Swiss St. Bernard head mark, and a maker's punch. Marks sit on the caseback outer edge or on the side between the lugs. They are stamped, so they have depth. Laser-etched fakes look flat under a loupe.

  • Look for the St. Bernard head, "750", and a maker's punch.
  • Check the crown and lug edges for color change that shows plating wear.
  • Plated brass shows a yellow-green tone and leaves a mark on skin.

Movement

JLC Master watches use in-house calibers. Caliber 899/1 runs the Master Control automatic. Caliber 925/1 runs the Master Ultra Thin Moon. Calibers 891/2 and 938 appear in other references. These movements beat at 28,800 vph and the seconds hand hacks. Fakes use decorated third-party movements such as the Miyota 9015, Sellita SW200, or Seagull ST21. Check the rotor text, the balance bridge shape, and the depth of the engraving.

Dial and Case

Real Master dials use applied gold numerals and faceted gold hands. Dial text is thin and sharp. The moon phase sits at 6 o'clock on the Master Ultra Thin Moon, with a pointer date along the arc. Fakes print the disc and often fit a 24-hour subdial in place of the moon phase. Case flanks are polished. Lug tops are brushed on several references.

Serial and Reference

Modern references start with Q followed by seven digits. Older pieces use three-part numbers such as 140.8.98.S. Caseback engraving is filled and even on genuine cases. Shallow or uneven engraving points to a fake. The serial sits on the caseback, and the caliber number is engraved on the movement.

Weight and Size

18k gold has a density near 15.5 g/cm3. Brass used under plating is near 8.4 g/cm3. A gold case therefore feels heavier in the hand than a plated fake of the same size. Measure diameter and thickness with calipers and compare against the published spec for that reference number.

Verification

A JLC boutique or service center can open the case, read the caliber, and confirm the serial against factory records. This settles the question. Acid testing and tagging damage the case, so skip both.