Two of the twelve configurations this reference builds cannot be made twice, and both of them are shell. Mother-of-pearl is cut from a material with its own structure rather than finished to a specification, so the banding runs differently on every dial and no two examples are the same watch. Reference 278278 is the 31mm Datejust in yellow gold, carrying a fluted bezel, 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. Sixteen references at this size carry the ground and all sixteen carry it in exactly this arrangement, which puts the entire difference between them in the metal.
The case is solid yellow gold at thirty-one millimeters with the fluted bezel cut into the metal itself rather than fitted as a separate ring. The dial is a slice of white shell, thin enough to be translucent in places, laid over a base and finished flat. Nacre produces its color by refraction rather than by pigment, which means it takes a cast from whatever surrounds it, and a gold case with a gold bezel and a gold bracelet surrounds it with one warm tone from every direction. The shell reads warmer here than the same material does in a steel or white gold case, and there is nothing anywhere on the watch to pull it back toward neutral. Twelve round diamonds sit at the hours in gold settings matched to the case. On a surface already returning light unevenly, the stones are the only fixed bright points on the dial, which is what keeps the ring legible against a ground that never holds still. 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. The shell and the stones both change as the watch moves and they change for different reasons: one by refraction inside the material, the other by reflection off cut facets. They rarely peak at the same moment, so the dial has two independent sources of movement on it and no fixed relationship between them.
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 entirely by position, since a diamond in a gold mount carries no information about which hour it stands at. On this ground that matters more than it does on a printed dial. A shell surface 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 large enough and bright 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 nacre it is more visible than on champagne and less visible than on a flat white, because the ground beside it keeps changing while the disc does not. The practical consequence of choosing this dial is that the watch looks different in every light and different again from any other example of it, which is the appeal and also the reason photographs of it are unreliable. Two examples sitting 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 of them identical. At 28mm the same twelve settings appear on thirteen references, and two further references at that size take gold markers at three, six and nine set with nine stones instead. At 34mm there is another version of that three-marker idea 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 nothing but the reference number separates them in a listing. Within this reference the ground is one of ten configurations carrying stones on the dial. It is also one of two here that no two owners will have identically, the other being the black shell, on a reference that builds twelve configurations across nine grounds with only two plain faces among them. The ground also survives every change of case at this size without changing arrangement, which almost nothing else here does; silver, olive green and dark grey all take a second treatment on the yellow references and shell takes none.
This is the version for a buyer who wants the dial to be the variable rather than the specification. Everything else on the watch is fixed and repeatable: one metal, one bezel, one bracelet, one setting arrangement across sixteen references. The shell is the only element that arrived rather than being made, and in a gold case it is also warmer than the same dial in any other metal, so the piece has a softness the champagne and silver versions do not. Anyone buying it should look at the actual example rather than at a listing photograph, since the banding is the whole point and it will not match the picture. Anyone who wants the shell to read cooler should look at the same dial in a white gold or two-metal case. And anyone who wants a shell dial behaving in the opposite way should take the black one, built on this same reference, where the material darkens instead of brightening and the stones separate rather than joining in.
