LVMH Watch Week: Zenith Launches The Rainbow Chronomaster Sport
For LVMH Watch Week, Zenith presents a very upscale version of a major technical powerhouse.
The Rainbow Chronomaster Sport is, as they say, just what it says on the tin: a version of the Chronomaster Sport with a rainbow gem set bezel, powered by the 36,000 vph El Primero caliber. The El Primero is a movement unique in modern watchmaking – it was, in 1969, one of the first automatic chronograph movements and the first high frequency chronograph movement of any kind, from any manufacturer. The El Primero movement went out of production but was saved from oblivion by an order from Rolex, requesting a lower beat version of the movement for use in the Daytona and, thanks to a Zenith employee who had hidden the tooling necessary to make the movement in a storage attic at Zenith, the EP was put back into production and, modified somewhat for more rationalized modern production, it remains in production today and has become the cornerstone of Zenith’s in-house watchmaking.
The EP caliber may have been a revolution in technical watchmaking but in the Chronomaster Sport Rainbow, we have an exceptionally luxurious take. As the name says, the bezel is set with color-gradient sapphires, ranging across the spectrum from deep red to yellow, green, blue, purple, and pink; there are color matched sapphire indexes on the dial as well. This is a slightly different-than-usual rainbow bezel, with four sapphires of the same color and saturation set in ten different sections of the bezel, which are themselves separated by diamonds.
You might at first think that it’s an odd choice to use ten sections instead of 12, but there’s a reason – this version of the El Primero movement has a center seconds hand which makes one full rotation once every ten seconds (the original EP movement had a conventional, one minute center seconds hand, with subdials for the minutes and hours).
The EP caliber 3600, on the other hand, has a sixty second counter at 3:00 in addition to the ten seconds center chronograph hand, as well as a 60 minute counter at 6:00, with a running seconds hand at 9:00. This is achieved by using the movement’s escape wheel to drive the chronograph seconds hand, rather than the fourth wheel, as is the case in a conventional chronograph. The Rainbow Chronomaster is not being billed primarily as a technical achievement but it’s worth remembering that behind the glitter there is in this case, some serious technical watchmaking. The EP 3600 was introduced in the Chronomaster in 2021 and the original, non-gem set version used a bezel marked out in 1/10th/second increments, so the use of ten sectors of sapphires retains the functionality of the original bezel, albeit with slightly less visual resolution than the original.
Driving the chronograph off the escape wheel is more technically challenging than using the fourth wheel because the escape wheel is the last wheel in the going train. A watch movement train from the mainspring barrel through to the escape wheel, trades off torque for rotational speed as you go, so the escape wheel, which is the fastest rotating wheel in the going train, is also the one with the least torque, so “borrowing” some of that energy can produce an undesirable drop in balance amplitude if you’re not careful. Zenith gets around this partly through extremely precise machining, and also through the use of silicon for the escape wheel, which reduces its inertia.
Although the rainbow bezel is not a continuous gradient as seen in some other rainbow bezels, the same basic problems apply. The sapphires sitting adjacent to each other must be exactly matched in color and saturation and their geometry must be very exact as well, as they must fit perfectly next to each other and also fit properly within the bezel geometry. Color matching can be extremely challenging – gem-setters must sometimes wait for long periods of time for suppliers to have enough gemstones of the right color and saturation, and to get the right cut and color, it’s sometimes necessary to reduce the size of the stone significantly.
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The Chronomaster Sport Rainbow, ref. 45.3104.3600/21.M3100: case, white gold, 41mm, 10ATM/100M water resistant, set with 40 baguette cut “rainbow” sapphires and 10 baguette cut diamonds; dial set with 12 baguette cut sapphires. Movement, El Primero caliber 3600, with ten second center chronograph hand, 60 second counter and 60 minute counter, running at 36,000 vph with 60 hour power reserve. Price at launch, $112,1000. For more, visit Zenith-watches.com.