The Luminous material that was applied on Rolex dials throughout the decades has been a source of mystery and debate by aficionados ever since it became fashionable to collect Vintage Rolex. In addition to a good loupe and a UV light, the Geiger counter has emerged as an invaluable tool to help evaluate the material present on a given watch.


Some years ago, I added this resource to my watch toolbox with the purchase of a US-made CRM 100 Geiger counter.

In my endeavor to familiarize myself with this new tool, I took readings from a variety of known sources for comparison. As expected, watches with Radium have a substantially higher reading than Tritium luminous material. However, it was surprising to note the readings produced by Radium watches from the same period varied measurably.


To help me understand this phenomena, I did some testing of Radium both exposed and covered with material of varying thickness. I came to the conclusion that readings are greatly affected by slight differences in the thickness of the obstruction. I have documented this using the following demonstration.

Geiger Counter Readings


The Red Triangle bezel is circa 1958 still has some original Radium material that remains lodged inside a broken pearl that became the basis of this demonstration.

(1) The Geiger measurement of the uncovered Radium that was taken is surprisingly high, over 46 mR/hr. considering the small amount of material still left in the broken pearl.


(2) Geiger measurement was taken under a thin, 1.32mm, plastic cover. The amount of radiation was reduced by >80%.



(3) Geiger measurement was taken under a Small Crown #16 domed crystal, that cut down the radiation level by 58%, when compared to (2) the thin plastic cover and by almost 84% when compared to (1) uncovered.

(4) Geiger measurement was taken under a used Big Crown #18 domed crystal, which cut down the radiation level by another 40%, when compared to (3) the Small Crown #16 and by 95% when (1).uncovered

From these four readings, we can observe that the Geiger counter is greatly affected by obstructions of varying thicknesses. We can therefore surmise that results would also be different under other crystals.

It is also interesting to note that when using a different brand Geiger counter, in this case, a GQ-GMC-500+ made in China, I got vastly different readings. However, the reduced amount of radioactivity from the Radium covered is still greatly reduced which is still in line with expectations.

Rolex Radium & Tritium Geiger Counter Readings

Submariner 6204 circa 1953

Submariner 6204 circa 1954

Submariner 6538 circa 1958

Submariner 6536-1 circa 1959

GMT Master 1675 circa 1962

Submariner 5512 circa 1965

1 is intended for informational purposes only and is in no way sponsored, endorsed,

or affiliated with Rolex U.S.A., Rolex S.A. or any other Rolex worldwide subsidiary. © All Rights Reserved 2020