The short answer
A genuine Blancpain Fifty Fathoms ref. 5015 does not have a tritium dial. The 5015 is the modern Fifty Fathoms Automatique family, and those watches left the factory with Super-LumiNova. Tritium belongs to older dive watches from the 1950s through the 1990s, which carried markings like "T SWISS MADE T" or "SWISS T < 25". If a listing puts "tritium" and "5015" in the same sentence, one of those words is being used loosely. In practice it means the dial is a redial, a swap from another watch, or an aged replica dial built to look vintage.
What the 5015 really is
The Fifty Fathoms Automatique 5015 is a 45mm dive watch with a sapphire bezel insert, a screw-down crown, and Blancpain's caliber 1315 inside. That movement runs three barrels and a five-day power reserve, and most versions have a display back so you can see it. It is a big, heavy, modern watch. Nothing about it is retro the way a 1960s Fifty Fathoms is retro, and the reference debuted long after tritium was phased out of Swiss watchmaking.
What tritium means, and why the word gets abused
Tritium is a radioactive isotope that was mixed into lume paint until the late 1990s. Its half-life is about 12.5 years, so a real tritium dial from the 1960s is dark today. Collectors pay for the patina, the cream plots and the burnt hands, not for the glow. That market is exactly why replica dials get "aged" with heat, tea, or tinted lacquer and then advertised as tritium. When I handle one of these watches, the lume marking at the bottom of the dial is the first thing I read, before I even look at the case.
Checks that separate a real 5015 from a fake
- Lume marking. A 5015 should read SWISS MADE at six o'clock. If it reads T SWISS MADE T, that dial did not start life in a 5015.
- Glow behavior. Super-LumiNova charges fast under a phone light and burns bright green or blue. Tritium patina barely answers. Aged replica dials often glow weak or not at all.
- Dial furniture. Look at the printed numerals at the quarters, the date window between 4 and 5 o'clock, and the sharpness of the text. Soft, fuzzy printing is the giveaway on most replicas.
- Bezel insert. The modern 5015 uses sapphire. A fingernail should not scratch it, and tapping it should sound like glass, not plastic.
- Movement. Caliber 1315, five days of reserve. Wind it fully, set it down, and check it four days later. A fake will not make it.
- Case back. Reference, serial, and depth rating should be crisp and correctly spaced. Replicas get the numbering right and the spacing wrong.
Why the tritium story keeps turning up in replica listings
Vintage vocabulary sells. Sellers borrow words like tritium, patina, and tropical to make a modern watch sound rare, and replica listings borrow the same words to make a new dial sound old. A tritium dial on a 5015 is a contradiction, not a feature. Anyone who tells you otherwise either does not know the reference or hopes you do not.
Price and provenance
Genuine 5015s are expensive, and pre-owned prices track the market rather than the story in a listing. Box, papers, and a service history matter more here than on most dive watches, because the 1315 is not cheap to service. A "tritium 5015" at a bargain price is not a bargain. It is a warning.
Bottom line
Read the dial marking first. If it says tritium and the case says 5015, stop there. No amount of patina, paperwork, or seller confidence changes what Blancpain put on that dial in the first place.