Everything's Illuminated

by Craig Hester

With its surprising ferocity, the competition to make the best-lit dial leads one to think more is at stake than just telling time. In fact, it turns out even the most cursory look into the history of luminosity in watches reveals that, well, there actually is.
Reading the time when the lights are out, and the process of making that possible, is astonishingly, and without hyperbole, a matter of life and death. From the military battlefield, to the depths of the abyss, to the tragic lives cut short of the young women who painted their dials, watches that can be read in any light level are as integral to horology as movements.
It is an exceedingly complex industry that blends science, art and engineering in both tedious and spectacular ways. Producing stable, safe and effective materials to illuminate watches in the dark has been a 300-plus year quest ever since, in 18th century Europe, the English physicist John Canton first prepared his luminous pigment from oyster shells that reacted with sulfur.
Today, watch companies, material manufactures and collectors everywhere tout the light emitting properties of their timekeeping devices with pride as new advances are regularly achieved.
This series of articles is the culmination of original research through interviews with industry leaders in the manufacture of watches and luminous materials. Additionally, traditional research methods of digging through already published works were employed. What you are reading wouldn’t have been possible without the assistance of Ted Cossins and his website where he culled together a significant resource on the history and functionality of luminosity.
A retired British engineer and relative newcomer to horology, Cossins put his web-based article together because he was “dismayed by all the misinformation” he read on watch forums and other websites.
What follows is by no means intended to cover all aspects of luminosity, but to provide a broad, general overview that can be used to further your own exploration of the topic.

The earliest efforts
Like many of the world’s great scientific achievements, the history of luminous pigments began in Asia millennia ago with the Chinese discovering they could grind photo-luminescent jade and utilize it to craft glowing beads, wine cups and other ornamentations.
The first recorded use of luminous paint occurred roughly 1,000 years ago in Japan. Documents housed at the Palace Museum in Taipei, Taiwan, tell of the emperor Zhao Tai Zhong’s fascination with the cave painting of a cow that appeared only at night. The story goes that the cow couldn’t be seen in the daylight as it “went to the meadow for eating” and then “returned to the cave in the evening.”
According to research by Nemoto & Co., which currently produces luminous material in Japan under the trade name LumiNova, the emperor ordered his scientists to investigate. Their inquiries revealed that the cow “was painted with special paints made from shells of the sea” which led to its appearance only at night. Other similar stories chronicling the early proliferation of luminous paints, some combined with volcanic materials, are known from this time, with China and Japan developing the first known trade in illuminating substances.
About 700 years later, the Italians invented the first synthetic luminescent material from a compound of barium sulfide, christened the “Stone of Bologna” or “Sponge of Light.” Englishman John Canton then followed this with his production of sulfur-reacting, light-emitting materials. By the end of the 19th century, Swiss watchmakers were regularly treating the dials of watches with a natural luminescent paint created using the same techniques as the ancient
Japanese artists. 

The “Radium Girls”
Then along came radium.
      “We were not aware of the risks of radium,” sounds more like words that would be uttered by the surgeon general from a podium in Washington, and not those of Albert Zeller, the third-generation CEO of RC Tritec, Swiss makers of the trademarked Super-LumiNova materials. “It was actually used for health reasons at the time, and most thought it even had positive influence,” Zeller told iW.
Radium-226 is an alpha emitter with a 1,600-year half-life. In layman’s terms, that means it is radioactive—not at all good for you—and won’t decay for thousands of years. 
Unfortunately, when mixed with zinc sulfide, linseed oil and glue, it also makes an excellent luminous material for watches. The radioactive emissions of the radium excite the zinc sulfide to produce the glow.
In the early 1900s, a Tiffany & Company gemologist named George Kunz and a chemist named Charles Baskerville patented this mixture, after inventor William J. Hammer failed to grasp the importance of protecting his original 1902 concoction, which used Damar varnish rather than the linseed oil.  Hammer’s fascination with radium began that year when he visited Marie Curie herself in Paris and she gave him nine vials of the substance she had discovered four years earlier.
A protégé of Thomas Edison, Hammer eschewed the patent due to the scarcity and high cost of radium.  An important civil suit later vindicated him, citing that no subsequent radium-based luminous paint could have emerged absent his original work.  Hammer also has the distinction of creating the first colored and white luminous materials.
For the decade to follow, radio-luminescent paints saw little practical application in all but, not surprisingly, Switzerland.  Ross Mullner, author of Deadly Glow: The Radium Dial Worker Tragedy, notes that “there were so many radium dial workers in that country that it was common to recognize them on the streets even on the darkest nights, because of the glow around them; their hair sparkled almost like a halo.”
By 1914 the first U.S.-based company had launched in Orange, New Jersey, which by 1922 evolved into the U.S. Radium Corporation. Carrying the brand name Undark, the company applied the radium-based paints to watches, clocks, pens and house numbers among other items. The government issued watches to infantrymen during the First World War, utilizing Undark to make them readable at night.
To achieve this, U.S. Radium recruited an army of young women, mostly in their teens and early 20s, to hand-paint dials, attracting them with an above-average wage for comparatively easy work versus their other options of the day. The going rate for painting 250 dials a day was about a penny and a half per dial, which at that time was good money.