Afterglow: A 1967 Rolex Submariner Reference 5512 With Tritium/Zinc Sulfide Markers
by Boris Pjanic
In the 1960s, tritium/zinc sulfide replaced radium/zinc sulfide as the lume of choice for watch dials and hands because, while still radioactive like radium, tritium is considerably less toxic.
Tritium’s half-life is 12 years, which basically explains why that substance will no longer glow strongly after 40 to 50 years.
I recall when I first found a Rolex Submariner 5512 with tritium/zinc sulfide on the dial. It led to a major discussion on an Internet forum about whether the dial had been re-lumed or not.
Well, years later, we know a lot more: the dial has not been re-lumed and,is was an original tritium/zinc sulfide dial.
A brief history of luminescence in watches
Lume: short for luminous phosphorescent, the substance that glows.
Phosphorescent: a type of photoluminescence, which unlike fluorescence, doesn’t immediately emit absorbed radiation, but emits it slowly. Zinc sulfide is phosphorescent.
Photoluminescence: substance that absorbs light (photons) and then re-radiates them, e.g. Super-LumiNova
1902-1960s: radium/zinc sulfide
The invention of radioluminescent paint can be attributed to William J Hammer, who mixed radium (in the form of radium salt) with zinc sulfide in 1902. Radium is radioactive (with a half life of 1,600 years) and emits alpha particles that energize the phosphorescent zinc sulfide, causing it to glow.
Radium-based lume was phased out in the 1950s/1960s as it caused radiation poisoning in those working with the substance.
1960s-1990s/present: tritium gas and tritium/zinc sulfide
Tritium replaced radium in the 1960s. Like radium, tritium is radioactive. However, it emits beta particles that are not as dangerous as radium’s alpha particles. Like radium, though, tritium was usually mixed with zinc sulfide, though a few brands, like Ball, have used small tubes of tritium gas that function like miniature, self-powered, bright-green fluorescent tubes.
Tritium has a half life (time taken for the emitted radiation to halve in intensity) of 12 years as compared to radium’s 1,600 years.
While zinc sulfide does glow for a short while after being exposed to light, tritium (and radium) lumes glow 24 hours a day as the zinc sulfide is energized by continuous radiation.
The brightness of the lume usually fades because the radioactivity gradually breaks down the zinc sulfide’s phosphorescent ability.
1990s-present: strontium aluminate/Super-LumiNova
Discovered in the early 1990s, strontium aluminate, also known by the brand name Super-LumiNova, glows 10 times brighter for much longer than previous lumes. It also odorless, non-flammable, and chemically and biologically inert so, not surprisingly, has come to dominate lume in watches.
The difference between strontium aluminate and zinc sulfide is that strontium aluminate easily absorbs and stores light (photons) so that it can be charged from either sunlight or artificial light. It doesn’t need a direct radioactive source of energy.
I recall when I first found a Rolex Submariner 5512 with zinc sulfide on the dial. It led to a major discussion on an Internet forum about whether the dial had been re-lumed or not.
Well, years later, we know a lot more; and one thing that is now certain is that the dial had not been re-lumed, but that it was an original zinc sulfide dial.
I myself have only seen two Rolex Submariner Reference 5512 models with this kind of luminosity, though just today I happened to see an Omega Speedmaster 145.022 with a zinc sulfide dial.
This is a first for an Omega wristwatch as far as I am aware.
But back to the watch at hand. The Rolex Submariner Reference 5512 went into production in 1959 with eagle-beak crown guards, which later became pointed crown guards before evolving into the rounded crown guards as we know them today.
Early versions are increasingly rare, the the tritium/zinc sulfide version even more so. Though there are no official numbers available, I estimate that there are probably just a couple hundred 5512 models outfitted with tritium/zinc sulfide that have survived.
The example shown here made its way from the United States to a collector in southern Germany and then to me.
Because it no longer had its original 7206 Oyster bracelet, I decided to put it on a Zulu strap, thus lending the unique dial a unique fashion look to match. It looks controversial, doesn’t it?
In their days, the Rolex Submariner 5513 and 5512 models were delivered with a so-called “superdomed” Plexiglas.
This type of hesalite crystal had a more rounded, domed shape to it as opposed to the later, flatter ones.
The superdomed crystal gave the watch a much different look, elongating the indices around the periphery. I love those superdomed crystals although they are supposedly not very water-resistant. But then I would not go diving with such a rare vintage piece anyway.
As you can see from the photo, the watch glows for a short time after being charged as if it were part of a German Christmas market.
The Reference 5512 with tritium/zinc sulfide has four lines of writing on the dial, with the lower two lines displaying a silvery grey-blue hue, not white.
I’m sure you can imagine that it is a lot of fun, although sometimes quite challenging as well, to research vintage Rolex timepieces to make sure they are original. The most important part for me is that the dial and hands match, fit into the correct time period based on the watch’s serial number, and that the dial “smiles” at me. Then you will see a smile sweep across my own face as well.
You can read much more from Boris Pjanic on his own blog, www.watchesandart.com.
Disclaimer: the author is a vintage watch dealer and any timepieces discussed may be for sale. For more information on him and his business, please read Meet Quill & Pad’s Vintage Virtuoso: Boris Pjanic, An Expert In ‘Pre-Loved’ Rolex.
*This article was significantly edited on December 23, 2014 to include historical information about lume and correct errors; “zinc sulfide” lume was replaced with “tritium/zinc sulfide” lume.
Reference number: 5512
Case: 316 steel, 40 mm, water resistance 200 meters (660 feet)
Bracelet: original steel bracelet Reference 7206 at delivery
Movement: automatic Caliber 1520 with C.O.S.C. certification
Functions: hours, minutes, sweep seconds
Price: new in 1968 was between $200 and $300. Current estimated value without matching steel bracelet around € 8,000 (approx. $10,000). Including matching bracelet estimated value around € 9,500 (approx. $13,000). This watch is too rare to be found at auction, therefore no auction results.