A Brief History of the California Dial

The definition of a 'California Dial' is very simple. It is a watch dial that consists of half Roman and half Arabic numerals. Numbers 10 to 2 are Roman, 4 to 8 are Arabic with 4,6,9 & 12 changing design from brand to brand.

The two brands most associated with the California dial are Rolex and Panerai. Rolex first started making watches with california dials as early as 1934 with the Ref. 3595 bubble back watch. These bubble back watches are some of the coolest vintage watches that Rolex ever made. They may be small by today's standards, 32mm to 34mm, but they have so much character that you gotta love them. The pink gold hooded lugs, tonneau cases and bubbly backs are worlds apart from what Rolex makes now.

In 1936, the Italian Navy requested that Officine Panerai make a watch for a team of combat divers. It needed to be water and pressure resistant watch with a dial which was visible at night and under water. To go on a quick tangent, this does not mean this watch, the Ref. 3646, is the first dive watch. Yes, it was a watch made for a team of professional divers but it's design did not differ all that much from other watches of that era. Compared to the dive watches from the 1950s and 1960s like the Doxa Sub300T, the Blancpain Fifty Fathoms, the Omega Ploprof and the Rolex SeaDweller, the Ref. 3646 is a very different beast.

The thing is that Panerai didn't make watches. They made measurement instruments like depth gauges but no wristwatches. So they approached Rolex to make a watch to the specs needed by the Italian Navy.

 What Rolex made for Panerai  was the Ref. 3646, the first production model that Panerai would release. The Ref. 3646 used a 47mm Rolex Oyster case which had wire lugs soldered onto it. Inside the watch was the Rolex Caliber 618, a manual wind, 16 line movement with 17 jewels. The dial was actually two pressed closely together; the bottom coated in a layer of radiomir with the top fitted with cutaways in the shape of the numerals to allow the luminous paint to shine through.

There were very few Ref. 3646's with a California dial ever made. Out of the 27 known Type E's, 17 of them have a California dial. This makes them exceptionally desirable for collectors of vintage military watches, in particular vintage Panerai

Rolex would apply for a patent the half Roman and half Arabic in 1941 and it would be granted in 1942. The patent says that the thicker numbers made applying luminous paint easier but nothing more about the reasoning for the two different numeral types. The Ref. 3646 would be produced from 1938 until the 1950s with different design changes classified Type A to Type G. Decades later, Panerai would begin remaking the Ref. 3646 with the Radiomir 1936 being released in 2011. Several other remakes/re-editions of the Ref. 3646 have since been released.

Why is the California dial named the California Dial?

The short answer is that no-one knows. There are a few theories that have been tossed around the forums but at the moment that's all they are, theories.

Theory No. 1: Californians just loved the mixed numerals in the 1930s and 1940s

During the heyday of the 'California dial' when Rolex were producing a lot of bubble backs with it, it was apparently popular in California. The distributors of Rolex realized this and as it became a fashion icon in high demand in the Golden State, these dials were nicknamed 'California'

Theory No. 2: California dealers in the 1980s were selling lots of watches with this dial

Vintage watch dealers in the 1980s based on Melrose Avenue, Los Angeles were selling lots of bubble back watches with the half and half dials. These California dealers began to let other dealers across the country know that they were seeking more half and half dials to sell to clients. Over time, these dials gained the California

Theory No. 3: A California dial refinisher in the 1970s worked on a lot of half and half dials

This theory comes from James Dowling, famed watch author and dealer. Someone asked a question about California dials on a Timezone forum and Mr. Dowling responded with his theory of the origins of the California name.

In the 1970s, when the vintage watch boom started, a LA based dial refinisher, Kirk Rich, did some dials with this design. They became popular & many vintage watch stores in California sent their dials to KR. So dealers in the rest of the US & the rest of the world began to call them the 'California' dial

Unfortunately I wasn't able to find the original forum thread. This quote is taken from a post written by the original asker of the question. I emailed Kirk Rich about the James Dowling quote and they responded with:

As per your inquiry about the "California dial", yes, we indeed did coin the phrase for this type of dial refinish. Around the late 70's early 80's customers would ask us for the "California dial" when requesting a refinish. Basically it was because it was easier than saying "Roman Arabic" when describing the mixed number printing. Roman numerals on top with Arabic at bottom. We were pushing a lot of these so much that people from all around would just ask for the California dial when sending us work. 
I am the third generation here at the company. My father Lou is the current owner of the company. He has been working here since the late 70's. Before him my grandfather owned and operated it since the 1950's. The company has been around since 1926. We are and have been the oldest and leading dial restoration business in the world ever since then. 
Thank you very much for writing us and asking us about this. It's always been a quiet pride of ours about the California dial. Not many people know about it and very few ask us about it. 

So there it is, the mystery of the California dial solved. Theory number three was correct and the name comes from a popular dial refinisher from the 1970s. Is there more to this story that I haven't covered? Absolutely. There will be other sides to the story and probably someone who swears blidn that it was them who coined the term California dial, not Kirk Rich. So is the way of the world.