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Blog: Rolex Hermetic Wristwatches

Copyright © David Boettcher 2005 - 2024 all rights reserved.

First published: 10 April 2024, last updated 12 April 2024.

I make additions and corrections to this web site frequently but, because they are buried somewhere on one of the pages, the changes are not very noticeable. I decided to create this blog to highlight new material.

The article below is part of the page about Hans Wilsdorf and Rolex.

As always, if you have any comments or questions, please don't hesitate to get in touch via my Contact Me page.


Hermetic Cases

Jean Finger Patent 89276
Jean Finger Patent 89276: Click image to enlarge

In January 1921 Jean Finger, a watch case maker of Longeau, Berne, Switzerland, was granted Swiss patent number CH 89276 for a “ Montre à remontoire avec boitier protecteur” literally “a stem winding watch with a protective box”.

This design of waterproof watch has the virtue of simplicity. In fact it is brutally simple. The problem of sealing the hole where the stem enters the case was not solved, it was simply avoided. A small watch is placed inside a larger case that has no hole for a stem and no opening back. The one-piece outer case has a screw-down bezel and forms a complete hermetic envelope around the watch.

There is no gasket between the screw down bezel and the middle part of the case, so the degree of water resistance depends on the two mating surfaces being very flat, and on the tightness with which the bezel is screwed down. The seal between the two parts is therefore nominal rather than highly pressure resistant, but it is effective at shielding the watch from dust, moisture and humidity.

To wind the watch or set the hands, the outer bezel is unscrewed and the movement flipped out on a joint (hinge). This allows access to the crown so that the watch can be wound and the hands set.

Although it achieves the desired waterproof effect, there is a major drawback on that the bezel of the outer case has to be unscrewed every day so that the watch can be wound. Apart from being a nuisance to the owner, the case threads and the milling on the bezel can wear out from this continuous use, especially if the case is gold or silver which are relatively soft, so this was a far from ideal solution. However, despite the drawbacks a number of manufacturers including Zenith and Eberhard produced watches using this case design.

Jean Finger evidently retained faith in his design, because he applied for a patent on a slightly improved version of his original design on 2 February 1929 and was granted an additional patent Swiss patent number CH 138244, published 16 April 1930. The differences between the two designs are small, the later patent uses a bezel that screws into, rather than onto, the front of the case, which allows the joint between the case and the screw in bezel to be concealed, and a different way of attaching the movement hinge to the middle part of the case. By this time the end of the road for the design was clearly in sight, and watches produced to the later patent are rare.

Rolex Hermetic

Rolex Hermetic Face and Bezels
Rolex Hermetic Face and Bezels: Click image to enlarge Rolex Hermetic Case and Cuvette
Rolex Hermetic Case and Cuvette: Click image to enlarge Rolex Hermetic Movement
Rolex Hermetic Movement: Click image to enlarge

Wilsdorf must have liked the design of Jean Finger's hermetic case and come to some arrangement with Finger because Wilsdorf applied for a British patent on exactly the same case design on 26 May 1922, which on 10 May 1923 was granted British patent number GB 197208 for “Improvements in and Relating to Watches”. Wilsdorf's British patent doesn't mention Jean Finger, so the exact ownership of the patent is something of a mystery. It seems likely that Wilsdorf paid Finger a fee to use the patent.

Some hermetic cases bear the words “Double Boitier Brevet 89276” (Double Case Patent 89276), a reference to the Jean Finger patent. Some cases bear the initials JF showing that these were actually made by Jean Finger, but other case manufacturers such as the Borgel company of Geneva also made cases to this design. A virtually identical but completely unrelated design was also patented around the same time by Frederic Gruen in the USA in 1918, see Double Case "Hermetic" Watches.

A trademark “The Submarine” was registered in Switzerland by Hans Wilsdorf on 31 March 1922, which was soon after he had presumably come to some arrangement with Jean Finger. This name is also a bit of a mystery because a watch called the “Submarine” had been sold by Brook & Son of Edinburgh since 1915. Watches with hermetic cases were sold by Rolex under the name Submarine, but they were not made by Aegler and were not branded as Rolex watches. For more about these watches, see RWC Submarine.

Rolex watches with hermetic cases were made by Aegler from around 1922. The photos here, kindly provided by Gio who posts on Instagram as @orologeek, show one of these Rolex Hermetic watches. The overall watch diameter is 32.35mm and the movement is 21mm diameter, which is 9.3 lignes so this would probably have been called a 9½ ligne movement.

The first photo shows the case open with the outer and inner bezels removed. The owner would not normally remove the inner bezel when winding or setting the watch, which was done using the crown that can be seen adjacent to the 3 o'clock. The inner bezel has a small projecting tab between the 4 o'clock and 5 o'clock positions which, when the bezel is attached to the inner case, can be used to swing the watch out of the outer case on the joint at the 9 o'clock position.

The case has British hallmarks showing that it was made to be sold in Britain. At the time this watch was made, British retailers did not allow manufacturers, English or foreign, to put their names on watch dials, and it appears that the “Rolex” logo on the dial of this watch was added later.

The second photo shows the marks inside the outer case back and the inner cuvette.

The case has London Assay Office import hallmarks for sterling (⋅925) silver. The date letter is the Roman small Blackletter (Gothic) "h" of the London Assay Office hallmarking year that ran from 1923 to 1924. Date letter punches were changed at the London Assay Office when new wardens were elected at the end of May, so the London hallmarking year ran from June of one year until the end of May of the following year.

An item cannot be accepted at a British assay office for hallmarking unless it carries a sponsor's mark which shows under whose responsibility it is submitted. Note that the sponsor's mark does not show who actually made an item, that has never been its purpose. The sponsor's mark here is the “W&D” mark entered at the London Assay Office by Wilsdorf and Davis, who were importers and certainly didn't make watch cases. It is possible that the case was made by Aegler, who registered trademarks for watch cases in 1900.

The case back and cuvette also have the Rolex name and reference to 7 World's Records, which was used in Rolex watches from around November 1923 until 1926.

The case back and cuvette are stamped with the number 397, and Gio tells me that he has seen two similar watches with the same number, so this might be a reference number for the case type.

The final photo shows the movement, which is an Aegler Rebberg, the movement that was used in Rolex watches at the time. This movement is a Rolex Prima, a designation that Aegler appear to have begun using on higher quality movements supplied to Rolex from about 1923.

The movement has a jewelled straight-line Swiss lever escapement and 15 train jewels. The balance is a cut brass and steel bimetallic temperature compensation balance. The balance spring is thermally blued carbon steel.

There is no obvious mechanical or physical difference between ordinary 15 jewel and Prima grade Rebberg movements, but the legend engraved on the barrel bridge, “Timed 6 positions for all climates” shows that the movement received more adjustments than an ordinary movement. Adjustments were made by adding or removing mass from the balance so that the rate was the same in all positions, and adjusting the overcoil of the balance spring so that the rate was the same at different amplitudes, from the greatest amplitude with the movement horizontal and the mainspring full wound to the smallest amplitude with the movement vertical and the mainspring run down over 24 hours.

The six positions are the two horizontal positions of dial up and dial down, and four vertical positions; pendant up, down, left and right. The “all climates” means that the rate was checked and the adjustments done at two different temperatures to ensure that the temperature compensation was correct.

The use of two screws to hold the crown wheel to the barrel bridge is a notable feature that was granted Swiss patent CH 97101 in 1922.

If you have any comments or questions, please don't hesitate to get in touch via my Contact Me page.

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Copyright © David Boettcher 2005 - 2024 all rights reserved. This page updated April 2024. W3CMVS. Back to the top of the page.