Rolex Submariner Tropical "Rad-228" ref.5508 "Box and Guarantee" from 1958

From the possession of a collector, this rare 1958 Submariner ref.5508 was originally sold in Singapore by Chop Kwang Heng, renowned retailer.  Its glossy gilt dial features a chapter ring and has aged to a rich brown tropical tone.

The luminous material on this dial is an unusual radium compound, radium-228, also known historically as mesothorium. Rolex appears to have experimented with different luminous mixtures during the late 1950s and early 1960s. The radium-228 isotope has a half-life of approximately 5.75 years, far shorter than radium-226’s roughly 1,600 years. That rapid decay might have also translated to the glow in the dark capabilities and caused Rolex to stop using Rad 228 later on, though the radiation measured today can be compared to a 1970s Tritium Dial (Almost none). 

The exclamation-mark dials that appeared around the radium-to-tritium transition are found on examples of the 5508, 5512 and 5513. They reflect a period when Rolex was changing its approach to luminous material and its permitted radiation levels.

A Swiss patent filed in 1954 and published in 1958 discusses the use of water-soluble radium and mesothorium salts in luminous paint. It provides valuable context for the materials being discussed at the time, although it does not, by itself, establish the precise compound used on this particular dial.

Brand: Rolex
Model: Submariner
Reference: 5508
Year of Production: 1958
Case Diameter: 38mm
Crystal: Sapphire
Lume: (Radium-228)
Movement: Automatic
Bracelet Width: 20mm
Bracelet: Made in USA C+I (1977)
Box/Papers: Guarantee Papers and Box
Mechanical Warranty: 6 Months

Comments: Watch working properly. The handset has been color matched to the dial cream-colored patina, under UV light, the hands show no visible glow. Bracelet is later, from the 1970s.