On May 8, 1951, the mightiest man-made explosion the world had ever seen – unleashing the cataclysmic power of 225 kilotons of TNT – shook the Enewetak Atoll in the middle of the Pacific Ocean. Tiny amounts of tritium – which had cost the US millions of Dollars – were responsible for boosting the blast to this extent.
George, the experimental device set off by the US as part of Operation Greenhouse, was designed to validate the principles of nuclear fusion required for the development of thermonuclear weapons. Based on a conventional nuclear bomb, George had a small mixture of liquified deuterium and tritium placed at its core. Compressed by the enormous heat generated in the first milliseconds of the blast, the atoms in the mixture were forced to fuse with each other. As a result, a large number of high-energy neutrons were released increasing nuclear fission (splitting of atoms) many times over. This was the first time men had achieved nuclear fusion, the very process that occurs within the sun.
The US was under great pressure. In September 1949, news broke of a successfull nuclear test in the Soviet Union. Western intelligence analysts had not expected the Soviets to get a nuclear bomb before 1953.
In consequence, US President Harry S. Truman gave highest priority to the pursuit of thermonuclear weapons in order to stay ahead of the game.
Early calculations suggested that extremely large quantities of deuterium and tritium, both heavy isotopes of hydrogen, would be required as thermonuclear fuel. The biggest problem the scientists at Los Alamos were facing was, tritium was unobtainable at the time and this very fact delayed the process considerably.
Tritium could be produced in modified particle accelerators or heavy water-moderated reactors. To keep the production of tritium strictly military, US President Harry S. Truman ordered the construction of five specially designed heavy water-moderated nuclear reactors near the Savannah River, 25 miles (40 km) southeast of Augusta, Georgia, to produce the desperately needed tritium.
Built with the threat of a nuclear attack in mind, the US government seized 310 square miles (800 km2) of land and distributed the reactors randomly over the entire area with a distance of at least 2.5 miles to each other.
Two large artificial lakes were created to provide enough coolant for the reactors. The small town of Ellenton and around 6000 citizens living in the area had to be relocated.
The Savannah River Plant produced most of the western world’s tritium supply from 1955 until 1988, when the facility was shut down for safety reasons. Tritium production was relaunched in 2007.
Construction of the Savannah River Plant began in 1951. Until the first reactor (R Reactor) went critical in 1953, the tritium needed for Operation Greenhouse was produced at the Hanford Site in the state of Washington. The Hanford reactors had produced the plutonium-239 used in Fat Man, the atomic bomb dropped on the Japanese city of Nagasaki.
To produce tritium, the Hanford reactors had to undergo a number of modifications and production of plutonium came to a halt. The cost for rifitting the reactors was between USD 2 million and USD 5 million (USD 20 to 50 million today). By mid 1950, Hanford was ready to produce around 10 grams of tritium per year.
The production of tritium is a complicated process that requires massive investments and vast infrastructure which in those days could only be provided by large industrial powers such as the US and the Soviet Union.
According to the modern Panerai company, G. Panerai e Figlio patented a tritium-based luminous compound named Luminor in January 1949.
Where did the tritium for Luminor come from? Giuseppe Panerai did not have a nuclear plant in his basement, nor a particle accelerator. As a matter of fact, the first Italian particle accelerator AdA (Anello Di Accumulazione) was built in 1961. The first Italian nuclear reactors were completed by 1964 with the help of the American companies Westinghouse and General Electric.
How is it possible that Giuseppe Panerai – the owner of a modest mechanical precision workshop – had enough tritium at his disposal to experiment and create a tritium-based luminous compound while the most powerful nation on Earth was struggling to produce even smallest amounts of tritium?
The answer is simple. The story put forth by the modern Panerai company is pure fiction. G. Panerai e Figlio did NOT invent a tritium-based luminous compound in 1949. They merely registered the trademark Luminor which had nothing to do with tritium. The trademark Luminor remained in a drawer until around 1965, when Mr. Panerai created his own mixture following the introduction of tritium-activated compounds in the Swiss watch industry.
Panerai’s self-luminous compounds
Luminor, and earlier Radiomir, were self-luminous mixtures used by G. Panerai e Figlio over the course of time to illuminate all sorts of dials, calculating devices and other instruments.
Radiomir was a radioluminescent mixture which used radium-226 as an energy source to excite zinc sulfide (inorganic phosphor). Zinc sulfide emits light upon excitation by radiation. If exposed to sun or artificial light, it will glow for a short period of time.
Contrary to popular belief, Radiomir was never patented. Radium-based luminous mixtures were invented and patented by Dr. George F. Kunz (789811 and 789812) in 1903.
Link to patent: Luminous Composition
What Guido Panerai patented in 1915 were sights illuminated by radium-226/zinc sulfide powder enclosed in small, hermetically sealed vessels which made it possible to aim at targets in the dark. The name Radiomir is a combination of Radio (radium) and Mire (sights).
What Guido Panerai invented was basically this.
The picture below is an excerpt from Guido Panerai’s British patent application from August 1915.
Improvements in Sighting-devices for Firearms and Torpedo Tubes
This invention relates to sighting devices of the kind which are rendered luminous by the use of radium and has for its object to provide improved means for rendering such sighting devices luminous, the said devices being for the use in small arms, machine guns, ordnance and torpedo tubes so that these weapons can be fired at night with a greater degree of accuracy than heretofore.
Link to patent: Improvements in Sighting-devices for Firearms and Torpedo Tubes
Panerai’s RadioMire (radium sights), especially the torpedo aiming calculators, were famous in the Italian Navy. The name Radiomir became soon synonymous for Panerai’s radioluminescence.
Radium-226 is a highly radioactive isotop with a half-life of 1,600 years. In addition to alpha and beta rays, radium-226 emits also penetrating gamma rays which can pass through the human skin. When ingested or inhaled, radium is treated by the body as calcium and deposited in the bones (so-called bone seeker).
The world became aware of the dangers of radium-226 following a series of lawsuits against the American company US Radium Corporation in the late 1920s. Female factory workers responsible for painting the dials were instructed to lip-pointing the brush in order to paint with more accuracy. The consequences of ingesting radium-226 were catastrophic and most of the Radium Girls died a painful death. After this debacle, the conditions for workers were improved and special safety measures enforced.
Giuseppe Panerai was well aware of the hazards posed by radium-226. The radioactive mixture was therefore sealed deep inside the dial behind a thick layer of hardened resin (plexi).
The picture below shows the inner layer of a typical Radiomir dial from WW2. The damage caused by the radioactive material is clearly visible.
Besides the hazards related to radiation, radium-226-activated luminous compounds had another big disadvantage. The luminosity diminished fairly quickly due to the destruction of the zinc sulfide by the ionizing particles emitted by radium-226. Watch dials of this kind lost their luminosity completely after only three to five years. Radiomir dials had to be replaced periodically.
Ref. 3646 watches that remained in service after WW2 were updated with modern 1950s Radiomir dials at some point. The next picture shows Vice Admiral Ernesto Notari’s 3646 which is exhibited at the Navy Museum in La Spezia.
This watch is a perfect example for a timepiece that remained in service after the war. The original dial lost its luminosity and was replaced with a typical 1950s Radiomir dial.
During WW2, Notari was a SLC (Maiale) pilot. When Italy officially surrendered to the Allies in September 1943, Notari remained loyal to the King of Italy and enrolled with the Allies in the south to fight against the Nazis. After the war, Notari was assigned twice as commander of the newly formed assault units and reached the rank of Vice Admiral.
Luminor, on the other hand, was a modern compound with radioactive tritium as the energy source to incite zinc sulfide to glow. Compared to radium-226, tritium is more or less harmless, as long as it is not ingested or inhaled. The half-life of tritium is only 12.3 years. The low energy beta rays emitted by tritium cannot penetrate the skin.
Tritium, also known as hydrogen-3 (3H) is an isotope of hydrogen, a variant with identical chemical behaviour. More on this later.
In today’s Panerai model taxonomy, the name Radiomir is used to refer to watches with Rolex-style screw-down crown while Luminor is the name given to models featuring the iconic Panerai crown-protecting device.
This is an extreme oversimplification which has no basis in reality and disregards the true history of G. Panerai e Figlio. Here is why.
The first 6152/1 models with patented Panerai crown guard were supplied to the Marina Militare with Radiomir dials, as can be seen in the picture below from G. Panerai e Figlio’s photo archive. In the modern Panerai’s book, this is a Luminor but clearly, it features a Radiomir dial instead.
Here is another image from G. Panerai e Figlio’s photo archive. Depicted is a so-called Destro where the crown guard is on the left side of the case. This watch features a Radiomir dial as well.
Only a handful examples of Ref. 6152/1 featuring the famous crown-protecting device that retained the original Radiomir dials have survived. Most of these watches were updated with Luminor dials at some point in time.
The luminosity in radium-226-based dials had a lifespan of only three to five years due to the deterioration of the zinc sulfide. Since these dials had to be replaced periodically, the most plausible explanation for the existence of watches that retained the original Radiomir dials is, they were unlawfully taken out of service at some point (stolen).
Reference 6152/1 was produced by Rolex in 1955 and later customized by Panerai. To install the half-moon shaped crown guard on Ref. 6152/1 cases, Panerai machined the cases to create two flat seats on the rounded case, as pictured below.
The original screw-down crown was replaced with a spring-loaded crown.
Giuseppe Panerai filed the Italian patent application for the iconic crown-protecting device on November 30, 1955. Claims the crown guard was developed much earlier during WW2 are unsubstantiated.
Link to patent: Fluid-tight winding means for a keyless watch
The picture below shows a 6152/1 with case number 124777 featuring the Panerai crown guard. 124777 is a typical Rolex Oyster case number from 1955.
Rolex produced a total of around 500 pieces of Ref. 6152/1 with case numbers ranging from around 124495 to 124999.
The Luminor “Patent”
According to the current Panerai – a company created by Richemont from scratch after acquiring the rights for the name Officine Panerai in 1997 – Radiomir was replaced by Luminor in 1949. The following screenshot was taken from the history section of the current Panerai website.
PANERAI FOR THE ROYAL ITALIAN NAVY – 1949
RADIOMIR IS REPLACED BY LUMINOR
A new self-luminous substance, Luminor, supersedes the radium-based paste. Tritium (hydrogen isotope) based, this compound is protected by the patent filed on 11 January 1949 under the “Luminor” trademark. Officine Panerai draws inspiration from the name of its newly patented substance for its other historical model that follows the Radiomir watch – the Luminor.
To back this claim, the modern Panerai company refers to a “patent” filed on January 1949 but fact is, the mentioned document is NOT a patent for an invention but merely a trademark registration for the name Luminor.
Brevetto per Marchio d’Impresa is Italian for Registered Trademark. Products related to the name Luminor are listed as the following:
Merci e prodotti da contraddistinguere: prodotti sotto qualisiasi forma (solido, pasta, polvere, liquido) luminescenti, fluorescenti, forforescenti e simili (classe 49).
Translation: Goods and products to be distinguished: products in any form (solid, paste, powder, liquid) luminescent, fluorescents, phosphorescent and the like.
There is absolutely no mentioning of tritium or how the compound is made in this document. Let’s go back to Panerai’s claim:
Tritium (hydrogen isotope) based, this compound is protected by the patent filed on 11 January 1949 under the “Luminor” trademark.
The referenced document does not protect a specific compound as claimed by Richemont. It is just a trademark registration for products related to certain luminous compounds in general.
On page 17 of the current 2018 – 2019 catalogue, Panerai makes a similar claim:
In 1949 Officine Panerai patented a new self-luminous substance based on Tritium (an isotope of hydrogen). This compound was protected by a patent registered on 11th January 1949 under the name “Luminor”.
In a statement made on page 53 of the current 2018 – 2019 catalogue, Panerai goes one step further and claims Officine Panerai actually invented tritium-based luminous compounds, implying they also invented radium-based compounds:
The Radium-based substance initially used to make the dials perfectly visible in conditions of absolute darkness was progressively replaced by a new self-luminous substance based on tritium (an isotope of hydrogen) also invented by Officine Panerai: this was “Luminor”, a substance protected by a trademark registered on 11th January 1949 for “products luminous in any form, fluorescent, phosphorescent and similar” intented particularly for military use.
A closer look at the goods and products listed in the trademark registration related to Luminor reveals yet another important detail. Tritium is radioactive. A tritium-based compound is radioluminescent as per definition but this adjective is nowhere to be found in the trademark registration.
Goods and products to be distinguished: products in any form (solid, paste, powder, liquid) luminescent, fluorescents, phosphorescent and the like.
If the trademark registration was intended for a radioactive compound, radioluminescent would be the first thing to be mentioned.
Furthermore, if Luminor was already available in 1949, why do all references from the 1950s still have Radiomir dials, namely Ref. 6152 from 1953, Ref. 6154 from 1954, Ref. 6152/1 with Rolex screw-down crown from 1955 and the gigantic GPF 2/56 from 1956 made for the Egyptian Navy?
The next picture shows Admiral Amedeo Vesco’s Rolex-made 6152 from 1953 with Oyster case number 956638. All known examples of Ref. 6152 have Radiomir dials.
Rolex-made Ref. 6154 from 1954 with case number 9975XX. There are around 20 known pieces of Ref. 6154 and all of them feature Radiomir dials.
The next picture shows a Ref. 6152/1 with case number 124547 made by Rolex in 1955. Ref. 6152/1 has lower case numbers than Ref. 6152 and Ref. 6154 because Rolex started from zero when they reached 1 million in 1954.
This very watch was on the wrist of an Italian Navy diver when he died during an underwater exercise off the coast of Sicily in 1957. The dial of this watch cleary says Radiomir.
The following Ref. 6152/1 watch was sold at Sotheby’s in October 2019. It was purchased from Panerai in 1958 and still featured a Radiomir dial.
This timepiece is accompanied by a letter from the Centro Subacqueo ed Incursori “Teseo Tesei” (precursor of ComSubIn) stating that Lieutenant Giuseppe Rasenti acquired the watch from Panerai in March 1958.
Si dichiara che il Tenente di Porto Sig. Giuseppe RASENTI ha regolarmente acquistato dalla Ditta PANERAI di Firenze un orologio subacqueo “PANERAI”.
La Spezia, 10 marzo 1958
Translation: DECLARATION: We declare that Lieutenant Mr. Giuseppe RASENTI has regularly purchased from the company PANERAI in Florence a “PANERAI” diving watch. La Spezia, March 10, 1958
The GPF 2/56, Panerai’s first own timepiece created without any involvement from Rolex, was produced for the Egyptian Navy from mid 1956 onwards. All watches found in Egypt were equipped with Radiomir dials.
The pattern is very clear. Throughout the 1950s, G. Panerai e Figlio continued to use Radiomir dials. In recent years, the modern Panerai company promoted the fictional narrative that the references 6152, 6154 and 6152/1 with traditional hornlugs and screw-down crown were so-called Radiomir 1940 models, produced in the 1940s. The Rolex Oyster case numbers of these models however, bear witness that all of them were produced in the 1950s.
Certain models with tradional hornlugs and screw-down crown were found with Luminor or Marina Militare dials. Dials featuring Marina Militare engravings were made with tritium-based Luminor as well, except for a bunch of altered Kampfschwimmer dials from WW2 with fake Marina Militare engravings which were manipulated by Rinaldi and co.
The explanation for the existence of Luminor dials in Ref. 6152/1 watches without crown-protecting device is pretty simple. In these cases, the original Radiomir dials were replaced with modern Luminor dials at some point after 1965. As mentioned, the luminosity of Radiomir dials lasted only three to five years and the dials had to be replaced periodically.
To recapitulate, in 1949, tritium was NOT available, anywhere on planet Earth. After WW2, tritium was thought to be an important component for thermonuclear weapons and the Americans were struggling to develop such weapons due to the unavailability of tritium. It is physically impossible that Giuseppe Panerai had tritium in 1949.
Here is what really happened. Giuseppe Panerai came up with a cool name for a future product and had it registered. Simple as that. In the same breath, he also registered product names like Translux and Elux, all related to luminous compounds in general.
What is Tritium?
Tritium is a gas. It is an isotope of hydrogen, which is the most basic element on Earth. Isotopes are variants of a chemical element which differ in the number of neutrons in each atom. With only one proton, a hydrogen atom has the simplest nucleus known and is therefore the first element in the periodic table.
Hydrogen exists in two other isotopic forms with identical chemical behaviour as hydrogen itself. Deuterium or hydrogen-2 (2H), which has a neutron in addition to the proton and tritium or hydrogen-3 (3H), which has two neutrons and one proton.
With two neutrons and one proton, tritium is the unstable isotope of hydrogen, thus radioactive with a half-life of 12.3 years. Tritum decays into helium-3 (3HE) with a yearly rate of 5%. Unstable isotopes have the tendency of converting into stable isotopes by releasing energetic particles in the process. The particles emitted is what causes radioactivity.
Hydrogen is one of two components of water. Water molecules (H2O) consist of two hydrogen (H) atoms and one oxygen (O) atom. By replacing hydrogen with deuterium, water turns into so-called heavy water (D2O). Since each of the two hydrogen atoms has an extra neutron in its nucleus, heavy water is heavier than normal water. Accordingly, ice cubes made of heavy water sink in normal water. Heavy water is used as a moderator in nuclear reactors with unenriched uranium (uranium-238) to slow down neutrons and split uranium atoms more efficiently. Since unenriched uranium is easier to get, heavy water in large quantities is subject to government control in several countries.
Hydrogen atoms in water molecules can also be replaced with tritium. This type of water is referred to as super-heavy-water or tritiated water (T2O) and is of course radioactive.
The name tritium is derived from the Greek word tritos, which means the third.
Production History Of Tritium
Tritium or hydrogen-3 is extremely rare on Earth. The atmosphere has ony trace amounts which occur through interaction of cosmic rays with the Earth’s atmospheric gases.
Hydrogen-3 was first detected in the mid 1930s by Lord Ernest Rutherford, Mark Oliphant and Paul Harteck from the Cavendish Laboratory at the University of Cambridge after bombarding compounds containing deuterium with deuterons (nuclei of deuterium/hydrogen-2) in a particle accelerator.
Rutherford asked the Norwegian Norsk Hydro heavy water plant (Vemork hydroelectric power plant) to try and create tritium by electrolytic process but after processing more than 13,000 tons of heavy water, no tritium was found.
During WW2, the Norsk Hydro heavy water plant was sabotaged by the Allies to prevent the Nazis from developing nuclear weapons.
In 1939, using Ernest Lawrence’s cyclotron at the Radiation Laboratory of the Physics Department of the University of California at Berkeley, Luis Alvarez and graduate student Robert Cornog fired heavy water molecules at deuterium and discovered that hydrogen-3 was radioactive.
Lawrence, the head of Berkeley’s radiation library, recognized the potential significance of this finding:
Radioactively labeled hydrogen opens up a tremendously wide and fruitful field of investigation in all biology and chemistry.
Earlier in 1938, the German chemists Otto Hahn and Fritz Strassmann had succeeded in splitting an uranium atom. The process of splitting atoms became known as nuclear fission. Fears the Germans could weaponize this discovery led a group of Hungarian scientists – supported by Albert Einstein – to warn the US government Germany could be working on a nuclear bomb, a weapon with the destructive power the likes of which the world had never seen before.
The US government soon realized the threat nuclear weapons could pose and created the Manhattan Project, a massive research program in which the best scientists from all over the world came together to develop a nuclear bomb before the Germans.
Early in the Manhattan Project, the American-Italian physicist Enrico Fermi mentioned to his colleague Edward Teller that the temperatures developed by a fission bomb could possibly initiate nuclear fusion, the very same process that occurs within the sun. Teller immediately realized the potential of a nuclear fusion bomb.
There were fears a thermonuclear explosion could ignite the Earth’s atmosphere but these concerns were ruled out by careful calculations. Obsessed with the idea, Teller envisioned two concepts, the Classical Super and the Alarm Clock but the leadership of the program remained focussed on fission weapons.
The Manhattan Project succeeded in its task and on August 6 and 9, 1945, the US dropped the first nuclear fission bombs on the Japanese industrial cities of Hiroshima and Nagasaki.
After the war, Edward Teller remained hooked on the idea of creating the so-called Classical Super, with a primary fission stage igniting a secondary fusion stage. This concept required extremely large quantities of deuterium and tritium which would act as thermonuclear fuel. Under extreme heat and pressure, deuterium and tritium atoms would be forced to fuse and unleash the brutal force of the sun.
However, the developement failed to gain traction because tritium was unobtainable, even smallest amounts. Two solutions to solve the tritium bottleneck were discussed. The construction of specially designed reactors and the modification of Lawrence’s cyclotrons in Berkeley. Any way that tritium could be produced would be exorbitantly expensive.
In September 3, 1949, a B-29 Superfortress operated by the Air Force’s weather service carrying special filters designed to pick up radiological debris, detected radioactive traces on a routine flight from Japan to Alaska. It soon became evident the Soviets had detonated their first atomic bomb.
Analysts had not expected a Soviet bomb before 1953. An extensive espionage ring withing the Manhattan Project had provided the Soviets with detailed information of the American bombs.
As a result of the Soviet test, US President Harry Truman prioritized the pursuit of thermonuclear weapons. He ordered the construction of five specially designed heavy-water moderated nuclear reactors where the massive amounts of tritium calculated for the Classical Super would be formed by neutron bombardment of deuterium. In the meantime, small amounts of tritium to test the principles of nuclear fusion were produced at the Hanford Site which had to undergo extensive refitting to do so.
Beginning April 1951, at the remote Enewetak Atoll in the middle of the Pacific Ocean, the US conducted Operation Greenhouse, a series of tests that would lead to the first thermonuclear shot. The picture below shows VIP spectators witnessing the detonantion of the Dog device, a conventional fission bomb with a high yield of 81 kilotons of TNT.
On May 8, 1951, the feasibilty of nuclear fusion was proven when the George device exploded with a yield of record-breaking 225 kilotons of TNT. George had a liquified deuterium-tritium mixture at its core. When the atoms fused, countless free neutrons were released which helped increase the efficiency of nuclear fission many times over.
A few days later on May 24, 1953, the so-called Booster, a compact device named Item with considerably less fission fuel than George was set off. Small amounts of deuterium and tritium injected as gas into the a cavity at the center of the fission fuel nearly doubled the efficiency of the nuclear fission reaction due to the release of a large number of high-energy neutrons.
Teller and his fellow scientists soon realized lithium deuteride would breed tritium on its own under the extreme heat and pressure of the primary stage. Prefabricated tritium was no longer required as fuel for the secondary stage. This discovery led quickly to a feasible two-stage concept known as Teller–Ulam design.
On November 1, 1952, the US tested the first full-scale thermonuclear device. Weighing 82 tons, the device named Mike was not a deliverable weapon and resembled more a laboratory than a bomb.
Mike’s thermonuclear fuel consisted of liquid deuterium which had to be kept in cryogenic state to avoid evaporation. The primary goal was to create the first multi megaton-explosion. The energy released was only limited by the amount of liquid deuterium.
The result was a 10.4 megaton explosion (10.4 million tons of TNT). Mike’s blast was so powerful, the island on which the device was detonated was completely vaporized, leaving behind a crater with a diameter of 1.9 km (6,000 ft) and a depth of 50 m (164 ft). Compared to the Hiroshima bomb, Mike was 650 times more powerfull.
Tritium remained nevertheless a crucial component to boost the primary fission stage of thermonuclear weapons which ultimately led to an extreme miniaturization of warheads, small enough to be deliverable by intercontinental ballistic missiles.
A modern Trident 2 submarine-launched ballistic missile can carry up to eight W88 thermonuclear warheads, each with an estimated yield of 475 kilotons and independently targetable.
Since tritium decays into helium-3 with a half-life of 12.3 years, accumulated helium-3 needs to be removed periodically while at the same time, tritium gas is replenished.
The US invested massively into production facilities for large quantities of tritium. Since tritium was no longer needed in the amounts as previously calculated, the US Atomic Energy Commission (AEC) became actively engaged in an isotope exchange data program and made tritium available to licensed parties.
New applications, especially in the area of biomedicine, were soon found. The beta particles emitted by tritium are of low energy and thus their penetrating range in matter is very short. This made tritium an ideal tracer to explore the mechanism of chemical reactions by tracing the path that the radioisotope follows within cells and tissues.
The first patent for tritium-based luminous compounds
It was in the above mentioned isotope exchange data program that tritium was found to be an ideal energy source for self-luminous compounds for watch dials and patented by Edward Shapiro on Oct. 29 1953 in the US.
The picture below shows an excerpt of said patent.
Tritium is particularly suitable as a radiation source for exciting the phosphor because of its availability at relatively low cost (currently 10 cents/mc.), and the extremely low penetrating power of the beta radiation therefrom. The latter feature permits the use of the tritium with a minimum of shielding for the safe handling thereof, thus rendering it particularly useful in applications where personnel are likely to be in close contact therewith.
Download patent: US 274951 – Source of Luminosity
This patent mentions the cost of tritium in 1953. The price was 10 cents per microcurie. In 1953, the amount of tritium needed for a mid 1960s Rolex Submariner dial with a maximum activity of 25,000 microcurie (Swiss – T <25) would have been USD 2,500. To compare, in 1954, the first Rolex Submariner was around USD 150. The tritium alone was 16 times the cost. The high price for tritium was probably the reason why watch companies were not interested initially.
The existence of this patent puts all claims to rest that tritium-based luminous compounds were invented by G. Panerai e Figlio. This document is also a great example on how patents are supposed to look. The compound and its production are described in detail over three pages.
According to information found on the website of RC Tritec Ltd., the Swiss company that produces Swiss Super-LumiNova, they started developing tritium-activated self-luminous compounds in the late 1950s.
Realizing the risk of radium, we started in the late fifties to develop a new self-luminous compound which was activated by Tritium to replace Radium completely. With its very low radiotoxicity and leaving no direct radiation outside of the watch, Tritium luminous compound was considered to be a perfect alternative.
The Strontium-90 Debacle
The Swiss watch industry introduced tritium-based lume following a number of lawsuits against Rolex in the United States of America. In 1959, the United States Atomic Energy Commission (AEC) found strontium-90 (90Sr) in Rolex 6542 GMT bezels. Strontium-90 is a radioactive isotope produced by nuclear fission with a half-life of 28.8 years. It emits almost exclusively beta rays. Since strontium-90 is a typical fallout product of nuclear explosions, its use is strongly regulated by the Atomic Energy Commission.
Following this discovery, several American customers sued Rolex for exposing them to dangerous radiation. The Atomic Energy Commission had not licensed the use of strontium-90 in watches or clocks. and interestingly, the AEC did not surveil the use of radium-226.
Rolex worked closely with the AEC to recall all 605 GMTs imported to the US and replaced the bezels. By the end of 1959 around 250 GMTs had been returned to Rolex. About three-fourths of them contained strontium-90.
Strontium-90 had a few advantages over Radium. It offered a greater variety of luminescent colours and the gradual decrease in luminous intensity was minimal since the beta particles emitted by strontium-90 did less damage to the zinc sulfide crystals. In addition, with 28.8 years, strontium-90 has a much shorter half-life than radium-226 with 1,600 years.
Following this debacle and mounting concerns among the population, Rolex stopped using strontium-90 and gradualy reduced the amount of radium-226 in dials until a viable replacement was found in tritium.
The next image shows the dial of a Rolex Submariner Ref. 5512 from around 1961. The word SWISS refers to the use of radium-226 in the luminous compound. The luminous dot underneath the 6 o’clock hour marker is apparently an indication for a reduced amount of radium-226. This type of dial is called Exclamation Mark dial.
In an ordinance from April 19, 1963 known as the Radiological Protection Act (814.50, Verordnung vom 19. April 1963 über den Strahlenschutz), the Swiss government banned the use of Radium in the Swiss watch industry. With the coming into force in 1964, working with radium-226 required a special permit, its use had to be justified and was subject to the control of the authorities. The act imposed radiation limits and radioactive substances such as tritium (hydrogen-3) had to be specified on the dials (T SWISS T). Special-purpose watches, such a diving watches, were allowed higher levels of radiation (SWISS – T <25 = activity lower than 25 millicurie or 25,000 microcurie).
The photo below shows a 1965 Rolex Submariner Ref. 5512 dial with tritium-based luminous compound emitting less than 25 millicurie, properly declared.
The British Ministry of Defense (MOD) established new standards for their timepieces. The type of luminous compound had to be indicated on the dials with a capital letter inside a circle. The picture below shows an Omega Seamaster 300 from 1967 featuring a dial with tritium-activated lume (T) specifically made for the Royal Navy.
Brands like Seiko or Blancpain (Tornek-Rayville TR-900) experimented with promethium-147, a radioactive isotope with a half-life of 2.6 years which emits low-energy beta rays but due to its short life span, the idea was not suitable for the mass market.
Ultimately, the Swiss watch industry went with tritium-activated compounds and sticked to them for almost forthy years.
In 1998, Rolex started using a new non-radioactive substance named Luminova developed by the Japanese company Nemoto & Co. in 1993. Luminova is a photoluminescent or afterglow based on strontium-aluminate. After being activated by sunlight or artificial light, the substance glows in the dark for hours. And this is where it gets interesting.
G. Panerai e Figlio created a photoluminescent compound named Translux before 1972. The flask pictured below was found in the basement of the Villino Panerai (Panerai Mansion) in Florence and has a G. Panerai e Figlio label on it. After Mr. Panerai’s death in 1972, the company was renamed in Offcine Panerai, so this is clearly from before 1972.
The product description stated on the Translux label resembles that of Luminova:
Pigmento luminescente cioè ritrasmittente di luminosità – per un breve periodo di tempo – se preventivamente esposto alla luce naturale od artificiale. NON AUTOLUMINOSO
Translation: Luminescent pigment therefore emitting luminosity – for a short period of time – if previously exposed to natural or artificial light. NOT SELF-LUMINOUS
If G. Panerai e Figlio developed Luminova-style pigments before 1972 – more than twenty years before the Japanese – that would be absolutely groundbreaking. It is interesting to see the modern Panerai company putting so much effort into perpetuating fictional narratives about the invention of tritium-based compounds when as a matter of fact they could have this amazing invention in their portfolio.
Translux was used for luminous discs installed on ships and submarines as emergency lights.
Panerai’s watch shop Orologeria Svizzera at the Piazza San Giovanni in Florence was a Rolex, Vacheron & Constantin and Longines retailer. When the Swiss watch industry switched to tritium-based luminous compounds around 1963/64, Giuseppe Panerai was one of the first to notice.
Radioactivity issues were soon discussed in Italy as well. In a decree from February 13, 1964 (D.P.R. 185) issued to protect workers and the rest of the population from dangerous ionizing radiation, the Italian government banned certain applications and established activity limits for watch dials. Interestingly, the Italian government continued to allow radium-226 if the activity was within certain limits. Regular watches were limited to 0.0002 millicuries while special purpose watches such as diver watches were allowed up to 0.0015 millicuries.
To compare, a WW2 Radiomir dial has an activity of 0.0013 millicuries measured through the crystal of the watch. For Panerai and the Marina Militare there was no need to react as Radiomir dials remained perfectly legal.
D.R.P 185 came into force in mid 1964. It can be assumed that even if Radiomir dials had a higher radioactivity than allowed, the Italian armed forces had not to comply immediately with the new law. Self-luminous dials with radium-226 were not only used in watches but also in all kinds of other military instruments like compasses, depth gauges, aircraft instruments, etc. Replacing all these applications was a galactic effort.
The very same limitations for radium-226 in watch dials were ratified in a ministerial decree from July 14, 1970.
The signs however were clear. The world was moving away from dangerous radioactive compounds and it was only a matter of time until radium-226 would also be banned in Italy.
Competition For Panerai
Around the same time, the Marina Militare started buying state of the art Eterna Super KonTiki diving watches with automatic movements and time-recording rotating bezels. Panerai watches had become hopelessly outdated.
The Eterna Super KonTiki Ref. 130PTX in the picture below is one of six diving watches that surfaced in La Spezia in 2017. All watches bear special markings on the casebacks and have case numbers that are within 27 numbers, making clear they belong to a special batch produced for the Marina Militare.
These watches were more versatile than so-called Panerai watches as they could also be used to time dives on compressed air as opposed to read time only. The dials had large tritium-based luminous plots and were perfectly luminous even in darkest condition.
Interestingly, an Eterna Super KonTiki or similar can be seen on the wrist of an Italian Navy diver on a photo printed in an Officine Panerai SpA company brochure from the 1990s.
In the mid 1960s, Panerai was sitting on hundreds of outdated Ref. 6152/1 watches and faced with a big loss, they had to come up with an idea on how to keep these watches relevant to the Italian Navy.
To be able to compete with modern automatic movements, Panerai decided to replace the original low power reserve Cortebert 618 calibers (36 hours) with Angelus 240 8-days movements.
Panerai had used these calibers for the first time in 1956 to power the gigantic GPF 2/56 (2/56 = 2nd project 1956) made for the Egyptian Navy. The Angelus 240 caliber was developed in the mid 1930s by Stolz Frères in Switzerland as a movement for table and alarm clocks.
For Panerai, Stolz Frères made a special run with 17 instead of 15 jewels. This was the first time an Angelus 240 was used in a wristwatch. The first movement batch was marked 12.55 (December 1955) on the main plate.
On page 108 of the current Panerai catalogue 2018 – 2019 it is written that Angelus 240 calibers were introduced at the beginning of the 1940s but there is absolutely no evidence to support this claim.
The only known 3646 featuring an Angelus 240 in combination with a Radiomir dial is a typical Rinaldi fake which was sold by Antiquorum in May 2004 (Lot 96). All other 3646s with Angelus 240 and Luminor dials are Rinaldi fakes as well. In my opinion, G. Panerai e Figlio never installed Angelus 240 movements in regular 3646 watches with wire lugs. Ref, 3646 was the only reference made in the 1940s. The first post-war reference was Ref. 6152 from 1953. Ref. 6154 came out in 1954 and Ref. 6152/1 in 1955.
The 2018 – 2019 catalogue also states Angelus movements were introduced to reduce wear on the threads of screw-down crowns. This explanation makes not much sense considering the GPF 2/56 and most of the Ref. 6152/1 watches featuring Angelus 240 movements have a crown-protecting device in combination with a springloaded crown.
Fictional narratives like this originate from Francesco Ferretti, a vintage Panerai dealer who became the modern Panerai’s consultant for history matters since 1997. His stories found their way unreflected into catalogues and promotional books.
Anyway, inspired by the Swiss watch industry’s switch to harmless luminous compounds, Panerai’s modified 6152/1s were to include modern dials with a tritium-based mixture to create a contemporary timepiece. Replacing radium-226 with tritium was also a logical step to protect G. Panerai e Figlio employees from dangerous radiation.
An interesting discovery made at Ferretti’s amazing Panerai Museum in Montecatini Terme is the existence of a self-luminous emergency light disc engraved with Trilumen Panerai (far left). Trilumen appears to be a fantasy name composed of Trizio (tritium) and Lumen (unit for visible light emitted by a given source). Trilumen and Luminor on the photo below seem to be exactly the same while Radiomir (right) is considerably different in colour.
Was Trilumen perhaps the name originally chosen for Panerai’s tritium-based mixture but later replaced with Luminor for its sexier sound?
A New Generation Of Panerai Watches
To promote the new 8-days movements and Luminor, Mr. Panerai came up with a brilliant idea of modifying around thirty Ref. 3646 leftovers from WW2 and awarding them to high ranking officers of the Marina Militare. These watches would be a link to the glorious past of the original Decima MAS pre September 1943 and at the same time a demonstration of Panerai’s capability to provide contemporary tools.
The watch pictured below is such a timepiece. Based on the slimmest version of Ref. 3646 made by Rolex in 1944, Panerai removed the wire lugs and welded modern hornlugs onto the existing cushion cases.
The low power reserve Cortebert 618 (36 hours) were replaced with Angelus 240 8-days movement leftovers that had been ordered for the GPF 2/56. All movements found in watches that are undisputed are marked 12.55 (December 1955).
These were the first watches ever to carry the Luminor name. To sugar-coat the whole thing, these dials also bore for the first time in the history of Panerai the Marina Militare name. Another novelty was the small seconds hand at nine o’clock to immediately see if the movement was running.
The watch pictured above is part of the Archivio Storico Panerai, the vintage Panerai collection of the modern Panerai company. It comes with an undisputable provenance since it was part of a vintage Panerai lot consisting of six watches handed over to Richemont by the original Panerai company after the sale of the Officine Panerai name in March/April 1997.
1 – Orologio Luminor MM storico – Anni 50
Translation: 1 – Luminor watch MM historical – 1950s
In the above mentioned inventory list, the Pre Vendôme people described the watch as from the 1950s, which is incorrect. This erroneous assessment occured due to the simple fact that the Pre Vendôme guys had very limited knowledge about the time before Giuseppe Panerai’s death in 1972.
Similar wrong statements can be found in Pre Vendôme watch ads where it was stated Luigi Durand de la Penne wore a Luminor when he attacked the HMS Valiant in December 1941 or that the Luminor was designed in 1938.
Luminor, l’orologio degli incursori della Marina Militare, è tornato per farvi rivivere la sua leggenda. Progettato nel 1938 per i reparti d’assalto della Regia Marina, viene proposto dalla Panerai riprodotto sui disegni construtivi dell’epoca.
Translation: Luminor, the watch of the Navy raiders of the Marina Militare, is back to revive its legend. Designed in 1938 for the assault units of the Regia Marina, it is offered by Panerai, reproduced based on technical drawings of the era.
The Mare Nostrum prototype – which undoubtly is a 1950s design based on instruments from 1954 – was described as a prototype from 1943.
Giuseppe Panerai was born in 1903. With thirtyone, he had to take over the reins of G. Panerai e Figlio (Guido Panerai and Son) after the death of his father Guido. Giuseppe Panerai was a business owner of the old school who managed everything himself. With his death on February 7, 1972, all knowledge about the watches died with him.
Modified 3646s with welded hornlugs are sometimes referred to as Transitional 3646. This is a misleading name since they do not represent a transition from wire lugs to lugs carved out of the same block of steel as the case. As a matter of fact, there was no transition. The production of Ref. 3646 ended in 1944 and in 1952/53, Rolex made Ref. 6152, the first model with traditional hornlugs. Rolex had used tradional hornlugs in watches made for the civilian market since 1931.
Welded hornlugs 3646s were equipped with display casebacks to exhibit the new 8-days movements. All awarded watches were numbered (Matr. No 1 – 30).
Apart from the matriculation number, these casebacks feature another important detail which holds the answer as to what these watches were all about. See the large I in the center of the plexi?
To understand the meaning of the I it is necessary to look at the broader context in which these watches were made. These were the first watches to ever feature tritium-based Luminor dials and interestingly, some Luminor vials found at the Villino Panerai in Florence have labels featuring the very same I. Tipo I is Italian for Type I.
This is no coincidence. The I stands for innocuo, the Italian word for harmless, and refers to the new tritium-based luminous compound.
As mentioned earlier, there is a lot of confusion regarding these pieces. Some Panerai enthusiasts still believe these watches represent a transition between wire lugs and traditional hornlugs but one look at the movements is enough to understand they are not.
The picture below shows the Angelus 240 movement of Matr. No. 2, the lowest known example. The movement is clearly marked 12.55 (December 1955).
By December 1955, Rolex had already supplied Ref. 6152, 6154 and 6152/1, all with traditional hornlugs carved from the same block of steel as the case.
The picture below was taken in August 2019 at the newly established Panerai museum in the Panerai boutique in Florence and shows the modified 3646 handed over to Richemont by the original Panerai company.
The watch is wrongly described as Radiomir 1940 with traditional horn lugs milled from a single metal block.
This type of watches have hornlugs that were welded onto existing Ref. 3646 cushion cases from WW2. The lugs are clearly NOT milled from the same block as the case as described by the modern Panerai company.
Some examples which are not as perfectly finished as the piece from the Archivio Storico Panerai show pretty rough welding marks.
Around 30 pieces of these specially modified watches were assembled (Matr. No. 1 – 30) to be awarded to high ranking officers of the Navy and veterans of the Decima MAS or their families. According to Panerai – Una Storia Italiana, this type of watches with display caseback were never used in action (page 235).
G. Panerai e Figlio soon released a second batch featuring the very same modern ingredients (Luminor plus Angelus 240 plus display caseback) but this time based on Ref. 6152/1.
The next picture shows Matr. No. 56, a piece which was given to the family of Alcide Pedretti, a Decima MAS member who was killed – together with Teseo Tesei – during a failed Maiale attack on the British Naval Base in Malta in July 1941 and was awarded a Gold Medal of Military Valour post-mortem.
The second batch featured the very same 4-liner dial with Marina Militare Luminor Panerai engravings as the first batch based on Ref. 3646.
This type of watches were equipped with Angelus 240 calibers marked MAI.61 (May 1961). The date stamp on the movement main plate does not necessarily refer to the production date of the movement. It is merely the production date of the main plate.
These watches have almost identical display casebacks as the first batch and the I for innocuo (harmnless) is ever present.
The second batch consisted again of around 30 pieces (Matr. No. 31 – 60). The lowest known matriculation number is 35, the highest 57.
Giuseppe Panerai’s plan worked out. Thanks to this little bribe, the interest in Panerai watches was revived and new orders were soon placed. In addition, all Ref. 6152/1 watches that were already in service since the mid 1950s were updated with Luminor/Marina Militare dials once the Radiomir dials had deteriorated. This explains why some 6152/1 watches without the Panerai crown-protecting device feature Luminor/Marina Militare dials.
According to Panerai – Una Storia Italiana, the last order of Panerai watches made by the Marina Militare was placed on July 12, 1968. 21 pieces of Ref. 6152/1 with Angelus 240 movements and SMZ (Sommozzatore = diver) engravings were ordered (page 248).
There is one 6152/1 with case number 124982 featuring an Angelus 240 movement marked 12.55 (December 1955). Some argued this is the proof Luminor was indeed introduced in the 1950s and not in the 1960s. Well, it is not. The watch in question has a caseback with SMZ No. 186 engravings. This is the highest known SMZ number which was part of the very last 21 pieces ordered in July 1968. The movement was either replaced or they installed a leftover from the GPF 2/56 order.
The production of tritium is a complicated process that requires vast infrastructure like nuclear reactors or particle accelerators. Furthermore, tritium was unobtainable in 1949 which ultimately led to a massive delay of the first American thermonuclear bomb. Unless Giuseppe Panerai had a secret nuclear reactor in his basement, there is no way he could have obtained tritium in 1949.
The facts presented in this article speak for themselves. Panerai’s claim that the original company invented a tritium-based compound in 1949 has no basis in reality. The referred document is not a patent for a particular invention but merely a trademark registration without any mentioning of tritium.
Giuseppe Panerai came up with a cool product name and had it registered. Panerai continued to use radium-226 throughout the 1950s and early 1960s due to lack of alternatives, just like any other dial maker. When the Swiss watch industry switched to tritium-based compounds in 1963/64, Giuseppe Panerai understood the signs of the time and started developing his own tritium-based mixture using tritium compounds that were now available on the market.
In Italy there was no immediate need to replace radium-226 since it remained legal as long as the activity was within certain limits, even after 1970. Since tritium-based compounds were a viable replacement for radium and having the safety of his employees in mind, Giuseppe Panerai discontinued Radiomir. All new watches delivered to the Marina Militare after 1965 were equipped with Luminor/Marina Militare dials.
To me, more interesting than the whole tritium story, is the existence of Translux, Luminova-style pigments before 1972. If G. Panerai e Figlio developed such pigments so early on, this would truly be groundbreaking and worth focussing on.
Thank you for your interest.
The Panerai Time Machine
Panerai watches were shaped by historically important events. The timeline below represents the current state of research into vintage Panerai watches. Please click the graphic to download the highres version.
This timeline is available as a high quality print in two sizes:
- 120 x 68 cm (47 x 26 inch): EUR 85.00 (plus shipping)
- 150 x 85 cm (59 x 33 inch): EUR 120.00 (plus shipping)
Printed with HD Inkjet on heavy synthetic paper and laminated.
Limited edition: 50 pieces, numbered and signed by Maria Teresa Panerai in Giuseppe Panerai’s very own laboratory at the historical site of the Villino Panerai (Panerai Villa) in Florence: Sold out
More information: The history of Panerai watches at a glance