Quick answer

A Fifty Fathoms dial marked "T SWISS T" or "T SWISS MADE T" is tritium. Tritium has a half-life of 12.43 years. Lume applied in the 1960s through the 1990s has lost most or all of its glow. If the markers light up bright green after a UV charge, the dial is not tritium. That is the fastest single test. It is not proof of age or originality. Printing, case numbers, and the movement still need review.

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What tritium means on this dial

Blancpain used tritium paint on Fifty Fathoms dials until Swiss makers moved to Super-LumiNova in the late 1990s. The marking sits below 6 o'clock. Early dials read "T SWISS T". Later dials read "T SWISS MADE T". The paint is tritium, a zinc sulfide phosphor, and a binder. After 30 to 60 years the binder yellows and cracks. The glow stops.

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Checks that separate fake from real

  1. Glow test. Charge the dial with a UV light for 20 seconds. Dead or near-dead lume fits tritium. Bright glow does not. Super-LumiNova is the common substitute on counterfeit dials.
  2. Printing. Compare the "T" letter shape, spacing, and height against a documented reference of the same period. Fakes print the mark too large, too high, or with the wrong serif.
  3. Lume texture. Original tritium paint is thin, matte, and often cracked. Fake paint looks flat and even, or sits too thick.
  4. Hands and dial match. Tritium on hands and dial ages together. Mismatched color points to a rebuilt or fake watch.
  5. Case and caseback. Check serial and reference stamps. Engraving depth and font vary by year. The current reference 5015 runs an in-house calibre 1315 with a 120-hour power reserve. A counterfeit case will not hold those proportions.

Limits

Photos cannot confirm a dial. Lume color shifts with camera white balance. Patina can be faked with tinted paint or tea staining. Only an in-hand exam with a loupe, a look at the movement, and service records from Blancpain settle the question. A dead dial with correct print and a matching movement is the strongest evidence. Nothing else is conclusive.

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