Short answer
Almost every Fifty Fathoms listed as white gold on the replica market is stainless steel with a gold plating or PVD layer, not a solid 18k case. Solid white gold Fifty Fathoms cases come from Blancpain's own catalog and from a small number of custom builders who machine cases to order. If a listing claims white gold at a low price, you are looking at a coating. The steps below show how to confirm which one you have in hand.
What you need
- A kitchen scale that reads grams, ideally to 0.1 g
- A small neodymium magnet
- A jeweler's loupe or a phone macro lens
- Bright light you can angle across the surface
- A soft cloth and a plastic caliper
How to check the metal
- Weigh the watch head alone, without the strap. A solid 18k white gold case in the 45 mm Fifty Fathoms size runs far heavier than steel.
- Compare that number to the published weight of a steel Fifty Fathoms. A plated steel case lands within a few grams of the steel figure. A solid gold case does not.
- Hold the magnet near the case sides and the lugs. 18k white gold is effectively non-magnetic and gives no pull. 316L steel gives a faint pull at the lugs.
- Inspect the lug tips, crown guards, and case back rim under the loupe. Plating wears first at contact points. Bare steel or a yellow base showing through means plated, not solid.
- Set the case next to a known white gold ring or a steel bracelet. White gold is rhodium plated and reads slightly warmer and softer than steel. Plated replicas often look too blue, or too yellow at the edges.
- Read the case back. Genuine gold cases carry a purity stamp such as 750 or 18K plus a maker mark. Replicas usually print the purity mark with no maker mark, and the lettering sits flat.
- Angle your light across the engraving. Laser-printed text has no depth. Stamped or engraved marks show a wall and a floor.
- Measure the case across the bezel with calipers, crown excluded. A 45 mm Fifty Fathoms should read 45.0 to 45.4 mm. Odd dimensions point to a generic replica case rather than a gold build.
- Have the case back opened by a watchmaker. Solid gold cases use a thicker gasket and finer threads. Plated cases often use a thin gasket and coarse threads.
- Test water resistance only after every other check passes. A plated case with worn threads will leak.
Red flags
- A white gold claim at a price that cannot cover gold
- No purity stamp, or a stamp with no maker mark
- Weight within a few grams of the steel version
- Color that shifts at the crown or the lugs
- Magnet pull at the case sides
- A seller who will not send a weight or macro photos of the case back
Care notes
Rhodium plating on real white gold wears thin over the years and can be redone by a jeweler. Gold-plated replicas cannot be re-plated the same way, and abrasive polishing cloths strip the coating. Wipe the case with a soft dry cloth, keep it out of chlorine and salt water, and store it away from harder metals that can scratch the plating.