Answer first
A fake Vacheron Constantin gold watch is not solid 18k gold. Most copies use gold-plated brass, gold-plated steel, or tungsten with a gold layer. Plating runs 0.5 to 5 microns thick. A real gold case carries a struck Swiss hallmark. Copies carry laser marks or no marks.
1. Read the Swiss hallmark
Switzerland hallmarks precious metal cases. Since 1995 the official gold mark is the head of a St. Bernard dog. Pieces made before 1995 use the Helvetia head. The fineness number sits next to the mark: 750 for 18k, 585 for 14k, 375 for 9k. Vacheron Constantin uses 18k gold and platinum on some models.
A hallmark is struck with a punch. Under a 10x loupe the digits show depth, a slight taper, and a rim of displaced metal. Laser engraving looks flat and shallow. That difference is the fastest tell.
2. Compare case and movement numbers
Vacheron Constantin stamps a case number and a movement number. The two numbers differ on every genuine watch. Copies reuse one number in both places, or drop the numbers.
The Maison holds records from 1755. Its Heritage department issues an Extract from the Archives. That document lists the date of manufacture and the case material. If the extract shows a steel case and the seller claims 18k, the claim is false.
3. Test the metal
- X-ray fluorescence (XRF): A jeweler's XRF gun reads the top 5 to 20 microns. Thick plating over base metal can read as 18k. Ask for a reading after a file cut on the inner caseback.
- Specific gravity: 18k yellow gold measures about 15.5 g/cm3. Brass measures about 8.5. Steel measures about 7.9. Tungsten measures about 19.3, so a plated tungsten fake feels heavier than the real case.
- Magnet: 18k gold does not stick. Steel does. The test rules out a steel core and nothing more.
- Acid test: A scratch on the inner caseback plus nitric acid exposes base metal. The scratch leaves a permanent mark.
4. Run the gold math
18k gold holds 75% fine gold. A 100 gram case and bracelet holds 75 grams of fine gold, about 2.4 troy ounces. At a spot price above $1,000 per ounce, that metal is worth several thousand dollars on its own. A seller asking $200 to $600 for a solid gold Vacheron Constantin is selling plated metal. Price does not prove a fake, but it sets the floor.
5. Inspect the movement
Genuine Vacheron Constantin movements show hand finishing: Geneva stripes, circular graining, polished bevels, and black-polished screw heads. Copies use stock or Chinese movements with plated bridges and printed stripes. Check the balance cock, the screw slots, and the jewel settings. Sharp, uneven slots point to a copy.
Some Vacheron Constantin movements carry the Poincon de Geneve (Geneva Seal), inspected by Timelab since 2009. The seal covers finishing and timekeeping standards, not gold content. A gold claim still needs a hallmark.
6. Know the legal risk
In the United States, 18 U.S.C. 2320 makes trafficking in counterfeit goods a federal crime. Penalties include fines and prison terms, and repeat offenses carry longer sentences. US Customs can seize shipments. Federal rules bar marking gold-plated items as gold, and items under 10 karat cannot carry a gold mark.
Quick checklist
- Struck 750 mark plus a Swiss hallmark.
- Case number and movement number differ.
- Extract from the Archives matches the case number and material.
- XRF reading taken on a filed inner surface.
- Specific gravity near 15.5 for 18k yellow gold.
- Weight and price consistent with 75% fine gold.