Short answer
Almost nothing sold as a "white gold" Patek Philippe replica is made of gold. The case is stainless steel, brass, or sometimes tungsten, finished with rhodium or chrome plating that mimics 18k white gold for a few months and then wears through. Real white gold references such as the Calatrava 6119G, the Aquanaut 5168G, and the Nautilus 5811/1G cost five figures in large part because the case itself is a precious metal object. That is the test: the scrap value of 18k gold in a Nautilus sized case already runs into the thousands, so a $600 listing claiming white gold has answered the question for you.
Why a white gold fake is harder to pull off than a steel one
Steel replicas are a cosmetic problem. The base metal and the genuine metal look the same on day one. White gold is a materials problem, and materials are hard to fake at a distance of six inches.
Weight
18k white gold has a density near 15.5 g/cm3, roughly double that of 316L stainless steel at 7.9 g/cm3. In the hand, a white gold Calatrava or Nautilus feels dense and cold in a way a steel replica never does. This is the easiest check and it needs no tools beyond a comparison piece. Tungsten is sometimes used to fake weight, but tungsten is gray, brittle at case edges, and hard to finish to bracelet tolerances.
Color and plating wear
White gold is alloyed with palladium, silver, or nickel and then rhodium plated for a bright finish. The plating is thin. On a replica, wear shows up first on the crown, the lug edges, the caseback rim, and the clasp, where the coating rubs off and the base metal reads yellow, pink, or dull gray against the rest of the case. Nickel plated replicas also cause skin reactions in people with nickel sensitivity, which is a tell in itself. Genuine white gold, even where the rhodium wears, is white all the way through.
Hallmarks and engraving
An 18k case carries a 750 purity stamp plus a Swiss precious metal hallmark, and Patek stamps its own reference data on the caseback. Replica hallmarks tend to be stamped rather than cut with the depth and sharpness Patek uses, and the model and serial numbers are often laser printed in a font that is close but not right. Since 2009 Patek has used the Patek Philippe Seal on its movements in place of the older Geneva Seal, and the finishing and rate specifications behind that seal are published.
What the movement gives away
White gold references use in house calibers such as the 26-330 S C, the 324 S C family, or the 31-260. Replicas typically run a Miyota 9015, a Seiko NH35, or a Chinese copy of an ETA 2824, sometimes hidden under a decorative plate with printed Geneva stripes. Real Patek finishing means hand beveled bridges with black polish, circular graining, and interior angles that no stamping or printed decal can produce. Put a loupe on the balance bridge and the difference is obvious within seconds.
How to test a case that claims to be white gold
- Weigh the head and compare it against a known steel reference of the same model. A white gold case should come in at about twice the mass.
- Have a jeweler run X-ray fluorescence. It reads surface composition in seconds and identifies gold, rhodium plating, and base metals.
- Ask for a specific gravity measurement if XRF is inconclusive. Gold plating over a steel core still shows steel density.
- Loupe the hallmarks at 10x. Look for uniform depth, correct letterforms, and stamps that sit inside the metal rather than on top of it.
- Check the wear points under bright light. Yellow or dark gray showing at the crown and clasp means plating over base metal.
Legal exposure in the United States
Trafficking in counterfeit goods is a federal crime under 18 U.S.C. 2320. Penalties for an individual on a first offense reach 10 years in prison and $2 million in fines, and the statute covers labels and packaging as well as finished goods. Imported counterfeits are subject to seizure and destruction by U.S. Customs and Border Protection under 19 U.S.C. 1526, and there is no personal use exemption for trademark infringing merchandise. Separately, stamping a non gold item with a 750 mark or advertising it as white gold can violate the FTC's Jewelry, Precious Metals, and Pewter Industries Guides at 16 CFR Part 23.
The practical consequences matter too. Patek Philippe will not service a counterfeit, and authorized service centers may refuse the watch outright. No auction house or serious dealer will consign one. Insurance will not cover it. Outside the same gray channels that sold it, the watch has no resale market.
If white gold is what you actually want
Buy from an authorized dealer or a major auction house and get the Certificate of Origin, the box, and an Extract from the Archives from Patek. Pay for a pre purchase inspection if you buy privately. If you only want the look, a steel watch or an honest homage gives you the silhouette without a counterfeit's legal and resale problems, and it will still be serviceable in ten years.