Three grounds are built on all three of the solid gold references at this size and this is one of them. The Everose, yellow and white gold versions of the 31mm Datejust with a set rim carry nine, nine and thirteen dials, and they agree on only plain white, silver set with diamonds and white shell. Everything else divides by case temperature. Reference 278288RBR is the 31mm Datejust in yellow gold, carrying a bezel set with diamonds, and this configuration pairs a white mother-of-pearl dial set with twelve diamonds in gold settings, with no numerals on it, and a President bracelet. Shell is the ground the metals cannot disagree about, because it takes its color from whichever one it is put in.
The case is solid yellow gold and the bezel is set all the way round in place of flutes. The dial is a slice of white shell, thin enough to be translucent in places, laid over a base and finished flat. Nacre makes its color by refraction rather than by pigment, so it reports whatever surrounds it, and here it is surrounded by warm metal on every side: a gold case, a gold rim, gold mounts and a gold bracelet. The shell reads warmer in this reference than the same dial does in a steel or white gold case, and nothing on the watch pulls it back toward neutral. Twelve round diamonds sit at the hours in gold settings matched to the case, and the bezel carries its own ring outside them. The two sets of stones behave differently against a shell ground than they would against a flat one. Bezel stones flare in sequence on a curve and the dial stones light together, but the surface under the dial stones is itself changing, so the inner ring appears to move relative to its own background while the outer one moves relative to the wrist. The President bracelet is semi-circular three-piece links in the same gold, rounded across their width, and it is the only bracelet this reference offers.
Hours, minutes, running seconds and a date advancing in a single step at midnight. The self-winding movement in the 31mm case holds roughly fifty-five hours of running time, matching the 28mm references rather than the 36mm ones, which run a movement of their own. Nothing further has been added, and the dial is read by position alone, since a diamond in a gold mount carries no information about which hour it stands at. On shell that matters more than on a printed ground. Nacre has visible structure of its own, bands and figuring running at whatever angle the material was cut, and that structure competes with any small marker placed on it. The twelve settings are bright enough and large enough to stay ahead of it; a printed index would not be. The date window at three is the one interruption in the ring, and against shell it is more visible than on champagne and less so than on a flat white, because the ground beside it keeps changing while the disc holds still. The practical consequence is that this watch looks different in every light and different again from any other example of it, which is the appeal of the material and the reason a listing photograph should be treated as one sample rather than as the specification. Two examples set side by side will differ in where the bands fall and how much color moves through them, and neither is more correct than the other.
White mother-of-pearl is the most widely built ground in the range and it changes arrangement more often than any other. At 31mm it is a ring of twelve settings on sixteen references, every one identical. At 28mm the same twelve settings appear on thirteen references, with two further references there taking gold markers at three, six and nine set with nine stones instead. At 34mm a version of that three-marker idea appears with twelve stones. At 36mm the name covers three separate dials and at 40mm a fourth, built with baguette-cut stones rather than round ones. Five arrangements share one name, and only the reference number separates them in a listing. Within this reference the ground is one of ten configurations carrying stones on the dial, and one of two whose appearance cannot be reproduced, the other being the black shell. Those two are also the only grounds here that arrive rather than being made. The identical twelve dials are built on 278278 under a fluted rim, so the rim is the whole of the difference between the two references. On shell that difference is smaller than it is on the flat grounds, because a dial already changing on its own terms is less affected by what sits around it than a still one would be.
This is the version for a buyer who wants one variable element on an otherwise fixed watch. The metal, the rim, the bracelet and the setting arrangement are all determined; the shell is not, and no two examples will match. In solid yellow gold under a set bezel it is also the warmest reading of the material the model offers, since every surface around it is contributing warmth. Anyone who wants the shell cooler should look at the same dial in the white gold reference or in one of the two-metal cases. Anyone who wants the material to be the subject rather than a texture should look at the black version on this same reference, where nacre works in the opposite direction and gives back color only at certain angles. And anyone who wants this dial with a plain edge should take 278278, which carries it under flutes and leaves the stones inside the crystal as the only ones on the watch.
