Radiomir, the wonder material that turned out to be deadly

‘Radium serves you safely and surely. The power of radium at your disposal’ — Undark Radium Luminous Paint advert, 1921

Scientists seem to have a pretty good handle of what’s safe and what’s not these days. Seems like an obvious statement to make, but it only takes a short journey backwards in time to hit a point where the people at the forefront of scientific development were, in hindsight, killing people in the name of progress.

Marie Curie and her husband Pierre started this particular chapter with the discovery of radium in 1898, which earned them a Nobel prize each. A fascinating substance, Marie Curie said of radium: ‘We must not forget that when radium was discovered, no one knew it would prove useful in hospitals. The work was of pure science.’ This statement was sparked by the immediate and widespread use of radium in industry: as well as its trademark luminescence, the health benefits, as they were understood at the time, were limitless. Doctors stitched lumps of this exciting element directly to tumours, even injected it into the throats of children to cure inner ear infections. Health spas—yes, you read that right—used radium-rich water in baths as a treatment—presumably to give patrons a healthy ‘glow’.


One obvious use for radium was nighttime illumination. Any kind of dial—car, instrument, watch, you name it—got a splattering of the stuff. The benefits were obvious, and the seemingly innocent chemical was viewed by many businesses as an opportunity; one such business was to be found in the idyllic city of Florence. Although father Giovanni Panerai was content to continue selling other manufacturer’s pocket watches in his Florence store, son Guido had other ideas. His ambition lay in specialised diving equipment: anything from torches to compasses to depth gauges, and the icing on the cake was his own special compound, a glowing paint he called ‘Radiomir’.

(Watchfinder & Co. head watchmaker Tony Williams deconstructs a Panerai Luninor Submersible.)

Radiomir was patented in 1916, in time for the big break that would launch Panerai’s business into the stratosphere: a contract with the Italian Royal Navy to supply diving equipment . . . and watches. The diving equipment Panerai could do, the watches they could not, so Guido approached a watch manufacturer that, although barely ten years old, had wowed the industry with its high precision movements and ground-breaking water resistance. That watchmaker was Rolex. With the 1926 ‘Oyster’, with its shellfish-inspired screw-down case and superlative resistance to water, Rolex was the ideal manufacturer for Panerai’s watch. With the Oyster case and the Radiomir paint, the watch would be the perfect tool for the Italian Royal Navy frogmen.

The way Radiomir (or any other product like it) works is through a process called radioluminescence. A phosphorous compound such as zinc sulphide is mixed in with the radium, and is excited by the impact of radioactive particles emitted by the decaying element. Radium, with its half-life of 1,600 years and emission of gamma rays is not only a remarkable source of radioluminescence, but unfortunately also of death. The penetrative nature of gamma rays and the ability to cause damage at a cellular level mean that even short-term exposure can be catastrophic. Before the work of the Curies and the understanding of radioactivity (a term coined by Marie Curie herself), that radioactive glow that we now associate with horrendous mutation and death was not only an industry darling, but even provided a source of amusement. In the United States, factory workers who applied radium paint to watch dials—later known as the ‘Radium Girls’—painted their nails and teeth with the stuff, for fun. Little did they know that their humour would result in severe deformity, necrosis, and even death.


As radioactivity became better understood, the use of radium in luminescent paint was inevitably banned. This left Panerai with a problem: how to illuminate the dials of its instruments and watches. A radioactive element was still the only option of the time, but with a new understanding of radiation, they knew they needed one that emitted the less powerful alpha and beta particles. That element was tritium. The same phosphorous compound was used, resulting in a similar glow, but without the same levels of harmful radiation. Panerai called this new product ‘Luminor’. The tritium-based paint continued serving Panerai until 2009, when the Japanese-developed fluorescent alternative ‘Luminova’ took its place.

A century has passed since the discovery, implementation and subsequent prohibition of radium. Once believed to be a wonder material, now understood to be a deadly poison, it defined a generation, its diverse and widespread use a warning to scientists and industry leaders of today to pursue knowledge before profit. Next time you see the marking ‘Radiomir’ on a Panerai, think back to those that suffered and died at the hands of this lethal chemical—including Marie Curie, whose carrying of radium in her pockets sealed her untimely fate—and wonder: what do we do now that we will look back on in a century’s time and realise, with hindsight, we were doing so drastically wrong?

Andrew Morgan is the editor of Watchfinder & Co.’s digital publication The Watch Magazine. To find out more, and to browse a selection of fine pre-owned Panerai’s, visit Watchfinder.

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