Two Greek Letters and a Gold Bezel: The Rolex Datejust 1601 Two Tone Sigma Dial

Either side of the words T Swiss T, just beneath six o'clock on this Rolex Datejust 1601, sits a small Greek sigma, and together the pair certify that the hour markers and hands above them are solid gold. Most people never notice them. They are printed at a size that rewards a loupe more than a glance, yet they tie this watch to a precise moment in Swiss watchmaking: the early 1970s, when the industry began printing proof of precious metal on its dials just as quartz arrived to question what a mechanical watch was worth. Put that dial in a 36mm steel Oyster case under an 18 ct yellow gold fluted bezel and you have the two tone Datejust 1601 in one of its most telling forms.

The Datejust Began as a Birthday Present

Rolex turned forty in 1945, and Hans Wilsdorf marked the anniversary with a watch that is still in the Rolex catalogue more than eighty years later. The Datejust brought together the ideas Rolex had spent two decades building: the waterproof Oyster case of 1926, the Perpetual self-winding rotor, and chronometer-grade timekeeping, all in one watch.

A date in a window

Rolex describes the Datejust as the first self-winding chronometer wristwatch to show the date in a window on the dial, changing automatically as the day turned over, and Monochrome Watches' history of the model records the same milestone. The launch reference 4467 was cased in 18 ct yellow gold, and it arrived with a bracelet made for the occasion: five narrow links per row, named the Jubilee after the anniversary it celebrated. That bracelet is still the one most people picture on a Datejust, and it is the natural partner for a two tone 1601.

The cyclops joins the crystal

The next defining feature came in the 1950s. With references 6304 and 6305, produced between 1953 and 1957, Rolex added the cyclops lens that magnifies the date at three o'clock, according to Monochrome. Early buyers could still order a crystal without it, but the small bubble soon became as much a part of the Datejust's face as the date window itself. On a 1601 the cyclops sits on a domed acrylic crystal, as BeckerTime notes of the whole generation, which gives it a softer, more integrated look than the flat sapphire crystals Rolex adopted later.

A Bezel That Started as a Tool

Of all the parts on this watch, the bezel has the longest history. Rolex presented a fluted bezel on the Oyster in 1926, and its ridges had a job to do: they let the bezel be screwed tightly down onto the case, completing the waterproofness that gave the Oyster its name. Rolex's own account notes that since 1953 the fluted bezel has been friction fitted rather than screwed on, and that it is made exclusively in 18 ct gold or 950 platinum.

What began as a grip for a tool became a way of catching light. The fluting breaks the bezel into dozens of angled facets that reflect in different directions at once, so the ring around the dial stays bright even in dim light. In yellow gold, those reflections are warm, and they change the character of the entire watch. On a steel Datejust with a white gold bezel the fluting reads as texture. On a two tone 1601 it reads as colour.

Reference 1601: Two Decades of One Idea

The 1601 was the Datejust for most of the 1960s and 1970s. Monochrome dates its production from 1960 to 1981, Wristler from about 1960 to 1981, and Ottuhr from 1959 to 1977 with some examples running later. BeckerTime places the arrival of the five digit two tone successor, the 16013, at the end of the 1970s, with the generations overlapping for a time. The spread of dates reflects how Rolex worked in the period, retiring references gradually as cases, dials and parts were used up rather than on a single day.

Across that long run the essentials held steady: a 36mm Oyster case, a fluted gold bezel, an acrylic crystal with cyclops, water resistance of 100 metres according to Wristler, and a choice of Jubilee or Oyster bracelet. The details evolved. Monochrome notes that early examples wore pie pan dials and alpha hands, while later ones moved to baton hands and stick indices, the cleaner look that defines 1970s examples like this one.

What two tone means on a 1601

Rolex has a name for steel and gold together. It registered Rolesor in 1933, joining Rolex with the French word for gold, as Millenary Watches documents. Rolesor is a construction rule rather than an alloy or a plating: the bezel, the winding crown and the centre links of the bracelet are gold, while the case and the outer links are steel. On the 1601 a suffix identified the metal. Wristler records the steel and white gold version as 1601/4 and the steel and yellow gold version, the two tone watch discussed here, as 1601/3, alongside solid gold versions, and Ottuhr notes that the 1601's fluted bezels were made in 18 ct white, yellow or rose gold.

The logic of Rolesor is visible from across a room. Gold goes where light gathers and where the eye travels: the ring around the dial, the crown, and the spine of the bracelet. Steel takes the case flanks and the edges that absorb daily knocks. A two tone 1601 therefore reads as a steel watch with a gold line drawn through its centre, which is a very different thing from a gold watch with steel parts.

Inside the Case: Rolex's 1500 Series

Beneath the screw down caseback sits a movement from Rolex's 1500 series, the family that powered most automatic Rolex watches of the era. Sources differ on the exact designation for the Datejust. BeckerTime and Watch Guy describe the 1601 with calibre 1560 or 1570, while Monochrome, Wristler and Ottuhr's reference guide give the date variants 1565 and later 1575. Ottuhr's calibre guide explains part of the confusion, noting that the date and non date versions carried the same calibre designation on their bridges despite their functional differences. We record both readings rather than pick one.

What is not in dispute is how the later movement works. Ottuhr's technical guide gives it 26 jewels, a frequency of 19,800 vibrations per hour and a power reserve of around 48 hours, running a Glucydur balance with a Nivarox Breguet overcoil hairspring. The overcoil lifts the outer end of the hairspring so that it breathes concentrically as it expands and contracts, reducing positional error, the kind of detail that let these movements pass chronometer certification in volume. Ottuhr also dates the introduction of hacking seconds to around 1972, which stops the seconds hand when the crown is pulled so the watch can be set to the second. Watch Guy's service notes on a 1601 describe that hacking lever as simple and effective, and describe the date change as driven by a strong spring that builds tension through the day for a crisp jump at midnight.

The date is not quickset, so advancing it means turning the hands through each day, as Ottuhr notes. Quickset arrived with calibre 3035 in the 16030 generation, according to Monochrome, which places the 1601 among the last Datejusts where changing the date meant winding the clock forward.

The Sigma Dial

Two letters at six o'clock

The feature that gives this watch its name sits at the very bottom of the dial. Where a standard 1970s Rolex dial reads T Swiss T, a sigma dial reads σ T Swiss T σ, with a Greek sigma on either side, as Millenary Watches describes. The mark came from APRIOR, the Association pour la Promotion Industrielle de l'Or, a Swiss watchmaking collective formed to promote the use of gold. Bob's Watches explains that it certified the goods were of Swiss origin and contained solid gold to a set standard, and on Rolex dials it signalled that the applied hour markers and hands were gold. Bob's records a first use date of 25 February 1970, commercial introduction on 1 March 1970, and a United States trademark filing in August 1971 that was registered in July 1972.

Why gold needed a certificate

The sigma solved a practical problem. White gold looks very much like steel, and on a steel watch with white gold details there was no way to tell the metals apart by eye. The mark made the material a matter of record, a point Millenary Watches makes directly. On a two tone 1601 the sigma carries the gold story from the bezel and crown onto the dial itself, so every element the eye lands on first is gold and says so.

Rolex used the sigma on its dress and precious metal lines, including the Datejust, Day-Date, Date, Daytona and Cellini, while the Submariner, Sea-Dweller and Explorer of the period went without, according to Bob's Watches. The marking appears on Rolex dials from about 1970 until the late 1970s, with occasional earlier examples, which makes it one of the most precisely dated details a vintage Rolex dial can carry.

Gold against quartz

The timing is what makes the sigma more than a hallmark. In December 1969 Seiko released the Quartz Astron 35SQ, the first quartz wristwatch, as Epson's corporate history records. About two months later, the Swiss industry had a mark in use declaring the gold content of its dials. Luxury Watch Supply and Ottuhr both read the sigma as a response to quartz, an argument for the value of a Swiss mechanical watch made in materials, at the moment its accuracy was being overtaken by a battery and a vibrating crystal. The decade that followed, now known as the quartz crisis, saw the Swiss watch industry contract sharply as cheaper and more accurate quartz watches took the market. The sigma sits right at the start of that story, and this 1601 carries it on its face.

T Swiss T

The letters between the sigmas carry their own information. The T on either side of Swiss denotes tritium luminous material on the markers and hands, as Bob's Watches explains, the luminous compound of the period. Read together, the full line at six o'clock records country of origin, luminous material and precious metal in a dozen characters, a compact piece of documentation that no modern dial repeats in the same form.

A 1970s Datejust on the Wrist

The 36mm Oyster case is the Datejust's original proportion, the size BeckerTime records for the 1601 and its successors alike. The fluted bezel draws the eye inward to the dial, the acrylic crystal rises in a gentle dome, and the cyclops sits proud of it at three o'clock. The bracelets of the period were built from folded links, as both Ottuhr and BeckerTime note, lighter than the solid links Rolex adopted later, and they give the 1601 a looser, more supple feel than a modern Datejust.

It is a watch of its moment in the best sense. The sigma pins the dial to the 1970s, and the acrylic crystal and non quickset date belong to the last generation before Rolex modernised the Datejust at the end of the decade. Everything that made the model in 1945 is still here, and one small addition from 1970 records what the Swiss industry was thinking when quartz arrived.

Final Thoughts

What we love about this 1601 is that its most important detail is also its smallest. The fluted bezel began in 1926 as a way to seal a case. The Datejust began in 1945 as an anniversary watch. Rolesor put gold where the light falls and steel where the knocks land. And two small sigmas at six o'clock, printed in the first years of the quartz age, record that the markers and hands on this dial are gold, at the exact moment the Swiss industry felt it needed to say so. Few watches carry their own history printed on their face. This one does.

References

1. Rolex, Fluted Bezel: https://www.rolex.com/en-us/watchmaking/features/bezels/fluted-bezel

2. Rolex, Datejust collection: https://www.rolex.com/watches/datejust

3. Monochrome Watches, The History of the Rolex Datejust: https://monochrome-watches.com/rolex-datejust-complete-history/

4. Millenary Watches, What is Rolex Rolesor: https://millenarywatches.com/rolex-rolesor/

5. Wristler, Rolex Datejust 1600 vs 1601 vs 1603: https://wristler.eu/insights/rolex-datejust-1600-1601-1603-comparison

6. BeckerTime, Two Tone Rolex Datejust Compare: 1600, 1601, 1625 vs. 16003, 16013, 16253: https://beckertime.com/blog/two-tone-rolex-datejust-compare-1600-1601-1625-vs-16003-16013-16253/

7. Ottuhr, Datejust 1601: Complete Guide to Rolex Variants: https://ottuhr.com/complete-guide-to-the-rolex-datejust-1601/

8. Ottuhr, Rolex 1570 Caliber Guide: https://ottuhr.com/index/rolex/calibers/rolex-1570/

9. Watch Guy, Service Rolex Oyster Perpetual Datejust 1601 / Calibre 1570: https://watchguy.co.uk/service-rolex-oysterdate-1601-calibre-1570/

10. Bob's Watches, What Is a Rolex Sigma Dial?: https://www.bobswatches.com/rolex-blog/resources/rolex-sigma-dial-definition.html

11. Millenary Watches, What is a Rolex Sigma Dial? Complete Guide: https://millenarywatches.com/rolex-sigma-dial/

12. Luxury Watch Supply, Jargon Unlocked: The Rolex Sigma Dial: https://www.luxurywatchsupply.com/rolex-sigma-dial-glossary/

13. Epson, Seiko Quartz Astron 35SQ: https://corporate.epson/en/about/history/milestone-products/1969-12-35sq.html

14. Wikipedia, Quartz crisis: https://en.wikipedia.org/wiki/Quartz_crisis

• Case in great overall condition, light wear visible.
• Leather strap in great condition 

• Dial & hands great condition, hands have light oxidisation