On 30 May 1941, the Luftwaffe bombed Dublin, the capital of neutral Ireland, by mistake. The Allies evacuated over 10,000 troops from Crete under fire from the German invaders and, in Berne, a representative of the Rolex Watch Company submitted a dial design to the Federal Patent Office. The design was given patent no. 221,643 and shows a dial with Roman numerals for the 10, 11, 1 and 2, and Arabic ones for the 4, 5, 7 and 8. There was a large triangle at 12 and the other quarters featured a horizontal bar.

What the patent doesn’t show is the unique construction of the dial. Most Rolex dials of the period measured between 0.25mm and 0.5mm thick, while this new dial was just over 1mm thick, and prior to being printed, the outline of the indices were stamped deeply into the surface of the dial. These stampings were visible from the rear of the dial and the recesses themselves were over 0.5mm deep. After the dials were printed, the luminous mixture would be applied — the recesses allowing significantly more luminous compound to be applied to the dial than if it were just laid on the flat surface. And more luminous compound means more output of light.

It’s elemental

The luminous compound on a dial is actually made up from three components: the phosphor, which is the part that actually glows; the exciter, which is the part that makes it glow; and the binder to hold it all together. In this case, the exciter was radium (Ra) and the phosphor was zinc sulphide (ZnS), the binder was essentially just paint. Radium is essentially unstable and is constantly emitting radiation in the form of alpha, beta and gamma particles. When these hit a zinc sulphide molecule, they excite it, causing it to glow.

This continues 24/7 although the glowing indices are not visible during daylight. The constant bombardment of the zinc sulphide by the radium particles results in chemical changes to its structure, which means that after several years — despite remaining radioactive and still being hit by particles — it ceases glowing.

It is no coincidence that the opening paragraph talks about both World War II and these dials because, even though Switzerland was neutral in the war, the country continued to supply watches, clocks and gauges to both sides. Luminous watches were the norm for combatants and if an improved luminous dial could be produced, there were obvious commercial benefits for the firm that made it.

Look at the 1944 advertisement shown opposite, where the dial is referred to as “Error Proof”, meaning it didn’t matter in which position the dial was held, the user would always be able to know where the 12 was, due to the triangle there. Also worth noting is the description of the hands as “Error Proof” — nowadays, we tend to call them “Mercedes” hands, but once again, the purpose of the design is to make sure that the hour and minute hands are instantly recognizable and cannot be confused with each other.

The hour hand is, in fact, a more-modern version of the classic skeleton luminous hand used since the turn of the century. What is worth looking at, though, is how the minute hand differs from the one currently used on modern sport watches, which have parallel sides and a triangular tip. Here in its first iteration, the minute hand is almost sword-shaped and its sides angle outward, enabling it to have a much bigger triangular tip, all of which makes it much more visible under any lighting conditions.

Speed dial

The dial was patented in 1941 and seems to have come into use almost immediately. While there are watches that were made before this date fitted with this dial, my guess is that these dials have been fitted much later in an attempt to make the watch more saleable. It seems that this dial design had a quite short life, almost coinciding with the duration of World War II, as the latest watch I have found with this style of dial dates from 1947. I assume that it is this short run and, of course, its unique design, which accounts for its desirability still.

The original patent drawings on the following page show three alternate designs for the dial, where different-style indices are used at 12 o’clock, and where the Roman and Arabic numerals are more randomly mixed on the dials; but, as far as I know, none of them ever went into production. However, there were variations on the dial that did make the production line.

The first was that some dials were produced with silver and gold faces; these were obviously more “dressy” versions, as luminous indices work best against a black dial. The other slight variation was that the index at six o’clock changed from a horizontal bar, as at three and nine o’clock, to a luminous dot, as can be seen in some of the images here. But the biggest change came right at the end of production, when all Arabic numbers were used on a very few dials, the layout remained the same, with the triangle and horizontal bars for the quarters and the deeply recessed indents for the luminous compound still used, but by now, the market for smaller watches was disappearing.

All grown up

If the Roman/Arabic dial spent most of its time adorning small watches, it made one of its final appearances on the biggest wristwatch of all, the Panerai Kampfschwimmer, made for the German military during the final months of World War II. The Wehrmacht had won all its victories in the first half of the war by the mass use of armored vehicles with close air support — the so-called Blitzkreig (or Lightning War) — and so their need for small commando units to fight behind enemy lines was almost non-existent. But as the Allies advanced through the European mainland and toward the borders of the Reich, it became evident that there was now a need for such troops.

Germany’s ally, Italy, had long had such forces. The 10th Flotilla of the Italian Navy, known as Decima MAS, were specialists at asymmetric warfare, mostly fought below the seas. So the German Army sent some of its best swimmers and athletes to train with their Italian colleagues. Because of the long experience of the Italians, the new German trainees learned their trade using Italian equipment. And, once they had graduated and returned to Germany, they were issued with equipment bought from Italian suppliers. Amongst this equipment were wristwatches purchased from Panerai, which was the exclusive supplier of instruments to the Italian navy.

The watches issued to these Kampfschwimmers were Panerai ref. 3646, which were actually made by Rolex. Panerai made instruments, not watches, at this time and simply ordered the watches from Rolex. Later, Panerai watches used that company’s patented “sandwich” dials, which were signed “Radiomir”, but the very first of the watches used the Rolex Roman/Arabic configuration — although not the “Error Proof” hands.

Big in Japan

After the war, the Roman/Arabic dial seemed to fade out of sight, most likely on its way to oblivion, but then something strange happened in the 1980s to change all that. Japan’s central bank pumped trillions of yen into the economy and the retail banks then eased their lending criteria so that they could loan that money out. This easy money found its way into property speculation, which, in turn, drove up the notional value of all land and properties in Japan. At the height of the speculation in 1988, the land beneath Tokyo’s Imperial Palace was worth more than the land in California.

Because of the easy availability of money and the rising value of their properties, the Japanese began to feel rich and their corporations splurged on everything from art (the two most expensive Van Goghs went to Japanese buyers at this time) to real estate worldwide (they bought Pebble Beach Golf Course in California and Rockefeller Center in NYC) and movie studios (Sony bought Columbia Pictures). Japanese citizens experienced a trickle-down effect as they saw the value of their homes rise massively, sometimes by as much as 25 percent in a year. So they too embarked on a spending spree that just happened to coincide with the birth of the vintage-watch market. The new Japanese buyers favoured smaller watches — particularly the Rolex Perpetual of the 1930s and 1940s, otherwise known as the “Bubbleback”.

For reasons I still don’t understand, the Roman/Arabic dial became the dial of choice for the Japanese retail buyers, and so, Japanese dealers sought them out, but the supply was small and soon dried up. Most Japanese dealers who traveled to buy watches went to the west coast of America, particularly to Los Angeles. There were several dealers of vintage watches in LA and when the demand for these dials began to overtake the supply, one of them turned to a local dial-refinishing company, Kirk Rich Dial Corp., and had it overprint existing Rolex dials with the desired design. At this point, the Japanese buyers were unable to tell the difference between original and reprinted dials, so refinished pieces flooded the market and, because of their origin, they became known as “California” dials.

As the 1980s slid into the 1990s, the Japanese economic bubble collapsed, and with it, the market for Rolex Bubblebacks, and it was assumed that the Roman/Arabic dial had finally gone for good. In reality, it had only gone for about 15 years, because in the early part of the new century, two firms reintroduced the style. The first was the sister brand of Rolex, Tudor, who used the dial on various-sized watches: ref. 76200 as a 36mm Day-Date, and ref. 74000 in 34mm with just a date window at three o’clock. Not to be left out, the following year, Panerai — now part of the Richemont Group and heavily mining its heritage — brought out the PAM 249, an almost-exact replica of the Kampfschwimmer watch. While the Tudor watch has long since vanished from its catalog, Panerai keeps reissuing versions, which it (along with Tudor) calls the “California Dial”.

Even though the life of the dial on Rolex watches was comparatively brief — less than a decade — I would like to suggest it still lives on. Look at the dial on any Rolex Submariner or Sea-Dweller and you cannot but notice the influences of the “Error Proof” dial and hands of the early 1940s. The triangle at 12 o’clock is still there, as are the luminous bars for the remaining quarter hours, and 75 years after it was first introduced, the “Mercedes” hour hand is still going (and glowing) strong. All thanks to patent no. 221,643.