THE JOURNAL
By and large, the idea of things that glow in the dark is one that loses its wonder once we hit double digits. Not to deny the awesomeness of those green stars you had stuck on your bedroom ceiling when you were six years old, or the spooktacular skeleton suit you wore every Halloween. But, well, its appeal does eventually fade, in every sense.
At the same time, though, we take it for granted that most watches have some ability to be read in the dark. Whether you’re out stargazing, working the graveyard shift or simply want to know if the movie will end before your last train home, there are plenty of situations in which a luminous watch dial can come in handy (and when you might not want to reach for your phone). Yet, we’ll bet a good many of you don’t know that the history of this innocuous functionality is laced with death and destruction.
Natural radioactivity was first identified in Paris in 1896 by a physicist called Professor Henri Becquerel, who discovered that uranium salts would leave an impression on photographic plates. He shared the 1903 Nobel Prize for Physics for his discovery with Professors Marie and Pierre Curie, who had isolated the element radium. It wasn’t long before glow-in-the-dark paints were commercially available, mixing radioactive isotopes with naturally phosphorescent compounds like zinc sulphide. Phosphorescence as a phenomenon has been known to mankind for millennia, occurring in ancient Chinese and Japanese art, but relies on the energy in sunlight to emit a glow.
“Lume has become a fertile area for experimentation”
Prior to the 20th century, the question of making a watch glow in the dark didn’t arise for two reasons: the known phosphorescent materials were impractical for use on watch dials, and watches were still kept in your pocket, where they would have been unable to “charge up” with sunlight. So the first luminous watches used radium-based paint, and this is where things take a turn for the worse.
It was known fairly soon after the Curies’ discoveries that radioactivity could have adverse effects on the human body, but it was assumed – with some justification, however misguided we now know it to be – that the quantities in items such as watches would be too small to have an impact. That was true, in the short term, but anyone involved in the manufacture of radium dials was taking grave risks with their health. The infamous case of the “Radium Girls” exposed the severe danger the substance posed.
The women employed by the US Radium Corporation, New Jersey, licked their paintbrushes as they applied radium paint to watch hands and dials. In the early 1920s, some noticed pain in their jaws and teeth; examinations found their bones had been eaten away “as if by moths”. Five women sued the company, eventually receiving out-of-court settlements. By the mid-1930s, all five and dozens of their colleagues affected were dead. Manufacturing conditions were improved, but radium paint continued to be used on watch dials until 1968, when it was finally banned.
“Innovation, military science and industrial negligence has made possible the useful and spectacular designs we enjoy today”
It was replaced by tritium, an isotope of hydrogen that is sufficiently radioactive to create a glow, yet safe enough not to kill you. A byproduct of the Cold War, it was made available to the commercial market in the 1950s when the US nuclear programme, having struggled to create even a few grams for years, suddenly found itself with a surplus when test explosions were found to produce vast quantities.
By the late 1950s, tritium-based paints were developed by RC Tritec, the Swiss firm that today supplies lume to most of the industry. Watch companies used tritium for around 30 years, until a Japanese firm by the name of Nemoto developed LumiNova, a zinc-sulphide based paint that boasted a long-lasting glow once exposed to light, and emitted no radiation whatsoever. Since then, both Nemoto and individual brands have improved their products – the industry standard is an upgrade known as Super-LumiNova, while the likes of Rolex and Seiko have their own patented compounds. Meanwhile, lume, as it’s colloquially known in all its forms, has become a fertile area for experimentation.
It is this history of innovation, military science and industrial negligence that made possible the useful and spectacular designs we enjoy today. Some brands sandwich a layer of luminous material underneath the dial and expose it with stencil cut-out numerals, like Panerai. Others invert the idea, coating the entire dial in luminous paint and letting the numerals stand out as shadows – like IWC Schaffhausen’s new Pilot’s Black Aces model, or Bell & Ross’ “full-lum” Heritage. And HYT has infused luminous paint into the liquid it uses to denote the hours, making for a real visual spectacle as the glass tubes glow from within.
Elsewhere across the watch industry, brands have experimented with solid blocks of the stuff, and even created composite materials with luminous dyes running through them for fully glow in the dark cases. We think your six-year-old self would agree, that’s a pretty good party trick.