Tritium

From tritium to luminova, when looking at watch dials, we often come across a distinctive feature: luminescence. Behind this peculiarity lies a history of innovation and change, linked to the evolution of the materials used.

Tritium and Its Applications

Tritium is a radioactive material combined with phosphorous substances to create a luminescence visible even in the dark. Its introduction into dials represented a turning point in the watchmaking industry, allowing the time to be read even in low-light conditions.

Common Dial Markings

• “T SWISS MADE T”: indicates the presence of tritium with a maximum radioactive emission of 25 milliCuries.
• “SWISS T < 25”: specifies that the emission is less than 25 milliCuries.
• “T SWISS T 25”: indicates the maximum allowable emission of 25 milliCuries.

These markings not only provide information on the dial's composition, but also help place a watch in a specific historical period. Tritium in sunlight (ph: rolexhaven.com)

Evolution of Luminous Materials

The use of tritium and its application have changed significantly over time. Here's an overview of the main evolutionary stages:

Until 1965: Gilt Dials

• Features: The indexes were domed and textured, with a luminous material that briefly glowed green after exposure to light.
• UV light: They displayed a uniform green finish.

1967-1968: Transition Period

• During these years, two extremes can be observed:
  • Heavily domed indexes with a brief green glow.
  • Flat indexes with completely inactive luminous material.

1968-1975: Flat Application

• Characteristics: The layers of luminous material were thin and almost always non-reactive to light.
• UV light: They showed greenish or bluish crystals.
• Aging: The material tended to yellow over time.

Mid-1970s: Return to Structure

• Characteristics: The indices regained some structure, but no light response.
• Colors: The predominant shades were orange, brown, and yellow.

Early 1980s: New Mix

• Characteristics: The applied material was flat and shiny, with no light response, but sometimes with a slight hint of green.
• Rolex Luminova dial

Trizio3[/caption]Tritium Luminescence (ph: secondtime.com)

From Radioactive Materials to Modern Luminescent Materials

Before 1960, many dials used radium, an extremely luminous but highly dangerous material. Over time, tritium replaced it, ensuring safe and controlled luminosity. Today, non-radioactive materials like Luminova have taken over, while retaining historic designations like "Swiss" and "Swiss Made." Luminova (ph: watchcrunch.com)