Short answer
A fake Cartier Santos sold as 18k almost never has a solid 18k gold case. In replica listings the term 18k describes a gold color or a thin gold layer on steel or brass. Solid 18k gold costs more in raw metal than the full asking price of the watch.
Fake Cartier Santos 18k V10: What the Label Really Means
What 18k means
18k gold is 75 percent gold by weight. 24k is 99.9 percent. Three finishes appear in replica listings:
- Gold plating: a layer of 18k gold on 316L steel or brass. Thickness runs 0.5 to 5 microns.
- Gold filled: a bonded sheet of gold alloy. US rules require at least 5 percent gold by weight, marked as 1/20 12k or similar.
- Color match: a PVD coating in a yellow tone. No gold content.
The metal math
At $2,700 per troy ounce, fine gold costs $86.80 per gram. Gold prices move, so use the current spot price. An 18k alloy at that rate is $65 per gram. A 60 gram case holds $3,900 in metal. Add a movement, a clasp, and bracelet links. A replica priced at $150 to $400 cannot contain that metal. No seller absorbs the difference.
Fake Cartier Santos 18K V8: A Buyer's Reality Check
Weight and density
Density values matter more than photos:
- 18k gold: about 15.5 g/cm3
- 316L steel: about 8.0 g/cm3
- Brass: about 8.5 g/cm3
A solid gold case of the same volume weighs about twice as much as a steel one. You can test this at home. Weigh the watch dry. Weigh it again while suspended in water. Density equals dry weight divided by (dry weight minus wet weight). A result near 8 means steel or brass. A result near 15.5 means 18k gold.
Hallmarks and stamps
Cartier marks gold cases with 750, the Cartier name, a serial number, and Swiss or French assay stamps. The French eagle head mark applies to 18k gold. Swiss gold carries the Helvetia head. On replicas these marks are laser etched on the caseback only. The etch has no depth, the font differs from the genuine stamp, and inner surfaces stay blank.
Wear over time
Plating of 0.5 to 3 microns wears at contact points: caseback edges, the crown, link sides, and the clasp. Base metal shows through in 6 to 24 months of daily wear. Brass turns dark. Steel shows grey. A solid gold case shows no base metal at any point.
Tests a buyer can run
- Magnet test. Gold is not magnetic. 316L steel is weakly magnetic. Brass is not.
- XRF scan. This reads the surface only, so plating reports as 18k. Useful on a filed inner surface.
- Acid test. Requires a scratch on an unseen area.
- File test on an inner lug surface. Gold color under the file means plating.
Questions for a seller
- Is the case solid 18k, plated, or PVD?
- What is the plating thickness in microns?
- What is the case weight in grams?
- Which hallmark appears on the caseback, and does it appear on the inner caseback?
Listings that answer all four questions with numbers are rare. Listings that answer with the word 18k alone are describing a color.